All language subtitles for Undiscovered Worlds Mexico 2of2 BBC 1080p EN SUB_Subtitles01.ENG

There are still parts of
our planet...

..yet to be explored.

Descending!

These are remote and unforgiving
places...

I'm in.

..and the journey to reach them...

We're in very real danger of
getting trapped here.

..will push me
and a team of explorers...

Ugh. Ugh, ugh.

..to the limit.

HE SHOUTS

It looks like he's coming back.

The reward...

Amazing!

..breathtaking new discoveries.

When you're standing in a place
that no-one has ever stood before,

it's very, very precious.

This time we're in Mexico.

Somewhere deep in there

is probably the thing I'm most
frightened of in the whole world.

I'm entering the supernatural land
of the ancient Maya.

Clear rope!

We'll journey underground
into a secret underworld...

Look at that!

..the Maya called
The Place Of Fear...

..to learn how they lived....

I just feel I've been connected
back through time.

..and died.

It's a skull! There's a human skull!

This is more the kind of fear
that I had when I was a kid,

and I was scared of monsters
under the bed

and the stuff of nightmares.

I'm in the Yucatan Peninsula
in Mexico.

All the way to the horizon,
it's just completely flat,

and beyond the realms of
the village, forest -

just thick, dense forest -

and underneath that is a peppered
latticework of caves,

almost none of which have
ever been explored.

Many of these caves are flooded.

I've spent the past month
with Robbie Schmittner,

a world-leading cave explorer.

We've been mapping these caves
to help scientists better understand

how to protect the precious
fresh water they provide.

It completely blows my mind...

..to think that below...

..so much of the Yucatan are rooms
like this that nobody has ever seen.

HE LAUGHS JOYFULLY

While Robbie continues mapping,

I'm heading further inland to
explore a set of special caves.

The caves have played a unique part
in the mythology of the ancient Maya

for at least 2,000 years.

The ancient Maya believed
these caves were portals

to a supernatural underworld
called Xibalba, "The Place Of Fear".

HORN HONKS

The human history here in Yucatan
is absolutely fascinating.

I'm not an anthropologist
or an archaeologist,

but you've got to say,

it's one of the most exciting places
on the planet.

The Yucatan is rich in artefacts
left by the ancient Maya,

a civilisation which stretched
across Central America.

Scientifically advanced, they were
master astronomers and builders...

..but they had a dark side.

Spiritual beliefs led them
to carry out unusual

and often gruesome practices.

Many were performed in these caves.

To get a deeper understanding
of the Maya,

I want to explore them
and go further into them

than anyone has before.

To help me, I've chosen
an elite team.

Underwater camera operator
Katy Fraser...

That's very light.
That's going to fly.

..dive supervisor Scott Carnahan...

Who is it?

..and former Royal Marine Aldo Kane,

who has the challenge of
keeping us all safe.

Our journey begins at
a secret location.

I'm meeting an archaeologist
who'll take me to these caves.

Hey, Memo.

Guillermo De Anda,
also known as Memo,

is a world authority
on the ancient Maya.

This place is remarkable.

It's unbelievable, isn't it?

This is a sacred cenote
for the ancient Maya.

He's spent his career examining
the powerful relationship

the Maya had with these caves.

So this is where we're going,
down here?

This is where we're going today.

Shall we get the lid
off this thing? Yeah.

These ruins date back
a few hundred years,

but beneath this tumbled down well
is a submerged cave

that's much, much older -

one Memo thinks is a Maya portal
to the underworld.

It contains a sinister secret
that has helped Memo understand

how the Maya lived and died.

Whoa.

What's that,
about 15 or 20 metres down?

Yeah, it's about 15 metres
to the water.

Have you ever dived
in a well before?

I have never dived in a well
before, no.

It's working, so you're going to...
Stop.

If we lift this back a bit...

We had to get down the well

and through a hole into the roof
of the flooded cave beneath,

all in full dive gear.

Which, erm...?

Are these my cylinders here?
Those are my cylinders? Yeah.

Before we dive, there's another cave
just minutes away

that Memo also wants me to see -

more easily accessible,

he thinks it has a grisly
connection to the well cave.

So, Memo, is it going to be
any cooler inside the cave?

Yes. Much, much cooler.

Oh, that is good news.

I tell you, my English blood
doesn't like this at all.

I know. Even we Mexicans...

..feel really, really hot
this time of year.

Do many people come down here, Memo?
No.

Fortunately this is, like,
still very well preserved.

We're stepping right now, Steve,
on a Maya stone stairway.

Only a select few know the location
of these caves.

Secrecy is their only protection
against vandals.

So we're looking at a piece
of Maya history.

Seriously, I got a chill that
went up the back of my neck

as soon as I saw that.

They look like they were left
yesterday.

If you see, we call it
Little Hands Cave or Manitas,

because there's a lot of children's
hands.

And if you look towards
your right...

Whoa, look at those over there!
Positive handprints, yeah.

This is really pretty special...
Yeah.

..that these are the handprints
of a Mayan child

left over 1,000 years ago...
Yes, yes. ..and they're still here,

as crystal clear as if a child
just put their hand in paint

and whacked it on the wall.

It's interesting that I've seen
prints like this in many caves

around the world, in New Guinea
and Borneo and in Europe -

there's clearly something universal

about leaving your mark behind
like this.

Do you think that this is
like playing? Putting paint?

Or do you think that there could be
something more to it than that?

You know, we cannot disregard
that possibility,

but I don't think that
that was the case,

because right where you are,
if we look up...

..we should find some little feet,
maybe a one- or two-year-old.

So there's no way that a child

could have deliberately put their
hands and feet up there... Exactly.

..it had to be done...

..by someone else, by an adult.

I wish I could find exactly
what the purpose

or what the symbolism
or what the meaning of that is.

We believe it could be maybe
a signature of something... Yeah.

..or a reminder of an event,
or a rite of passage.

These might have been children
that were sacrificed afterwards.

It was part of a ritual.

That's an incredibly
macabre thought.

We're looking at the handprints
of a Mayan child

from well over 1,000 years ago

that may soon after have been
sacrificed.

Yes. Oh, yeah.

Yeah, maybe this was the
last thing they'd do in their life.

There are over 100 handprints
in this cave.

If Memo's theory is correct,

each one could belong to someone
who was ritually sacrificed.

There are even prints from
children as young as two.

If they were killed here,

their remains are missing
from this cave.

Memo believes the flooded cave
beneath the well

could hold the key to
understanding why.

He's been diving in
this well cave before,

and believes the site had a special

and grisly significance
for the Maya.

He thinks they came to
carry out human sacrifices.

That's pretty scary.

Effectively, we're going into
a sunken mausoleum.

It is the kind of stuff that wakes
you up in the middle of the night

in a cold sweat.

It is the stuff of nightmares.

It's not ideal to set up here
because of the distance.

We'll work that out,
or I can pull them in.

Aldo's rigged a frame
that will lower us

and our equipment into the cave

and, just as importantly,
get us back out again.

It is a complex operation.

We've got four divers in a confined
space in an overhead environment,

in a cave, and you're on the end
of ropes.

We can't get to you that quickly.

In fact, we probably won't
get to you -

it'll be down to you to
self-rescue to the ropes.

For once on an expedition,

I'm not thinking about
the logistical problems.

OK, lean out a bit further.
Try and get out past the edge.

Right, was there anything
that needed changed on that?

Nope, negative.

Everyone happy with how that went?

These caverns are living graveyards,
living mausoleums.

Two metres in the water.

This is more the kind of fear
that I had when I was a kid,

and I was scared of monsters
under the bed

and creatures in the cupboard.

It's that fear of the unknown,

and darkness and death,

and all the things that
haunt us most.

Katy?

The Maya feared these caves

because they believed the gods
responsible for human suffering

lived in them.

They offered these gods gruesome
sacrifices to try and appease them.

HIS VOICE ECHOES: Descending!

How far out are we, Scott?
More, Aldo.

OK, Steve, we're going to lower it
on the working line. So get down.

Diver on the bottom?
Diver's floating.

Stop.

All stop.

Guillermo? Guillermo, are you OK?

Can you hear me well?
Yeah, I can hear you.

Take your time and get
your systems right.

OK. Moving in closer.

We've been granted permission
to dive here

on the understanding that we don't
touch anything we find.

Guillermo, I see something.

OK.

It's a horn.

We're just descending down...

..underneath...

..the daylight...

..of the well above.

That is the skull of a bull.

What's this on the teeth, here?

Steve, I really don't know.

It looks like gold.

There is no natural goal
here in the Yucatan, is there?

No. No, Steve.

There is no gold in Yucatan.

The unusual appearance of
the teeth could be due to

natural discoloration caused
by the diet of the animal,

and this skull can't be from
the time of the ancient Maya,

because we know they didn't
have cattle.

OK. What do you think?
Shall we go down?

Let's go for it.

Look at that, Memo, it's a pot!

It's beautiful.

How old do you think this might be?

This might be 1,000 years old,

and look how well-preserved it is.

Wow.

They weren't just dropped in here
by accident.

No. No, Steve, it would be
too many accidents.

What would be in these pots?

Usually food or maybe
a sacrificed animal.

Maya pottery was extremely fragile.

What we found suggests someone
swam down and placed it here intact.

Guillermo, what's that?

Oh, where is it?

Just...just below you now,
in your torchlight.

Just there.

It's a skull. There's a human skull.

There's something very unsettling
about the sight of a human skull.

It might belong to somebody
that was high-class, elite...

How do you know that?

If you look closely at the teeth,

you can see they have been
modified for symbolic purposes

when this person was alive.

Memo thinks the person
was decapitated,

and the head or skull then used
as an offering.

There are bones everywhere.

Arms, legs, ribcages, feet -
all given to appease the gods.

This is without any doubt
a very sacred place.

Ancient Maya artwork shows that
sacrifices were incredibly gruesome.

Flesh was stripped from dead bodies,

and they even inflicted
terrible injuries on themselves

to offer up their own blood.

What's that? What have you got?
It's a complete body.

How he got there, I wonder...

Memo has come across
this sort of thing before.

I have seen evidence of
cut marks, very deep,

either on the ribs...

..or either in the sternum.

That tells me that a knife
got in that body

and very skilfully ripped apart
the heart.

Sometimes this happened
when the victim was still alive.

They ripped out their hearts
and they were still alive?

Yes.

Those are...
Those are under an overhang.

Yes. It looks like they were
placed there, Memo.

There's no current in this chamber,

and all the bones are arranged
close to each other.

They may have been put here
deliberately -

no easy task.

It was hard enough for us to get in

with modern ropes
and climbing equipment.

They would have had to
hold their breath

and swim down to place this
offering here,

to push and prod it
into this position.

Everywhere you look,
there's another body -

another skull...grinning at you
from the darkness.

This place has so many stories
to tell.

So many secrets,
so many mysteries...

Everywhere you look, the memories
of an uncomfortable ritual past.

This place has horrifying
nightmare significance.

The cruelty the Maya engaged in
to appease the gods of Xibalba

is evident everywhere.

These barbaric acts seem at odds
with the sophistication

of their culture.

What we hear about the ancient Maya
is all quite macabre.

It's all about human sacrifice
and kind of quite grisly.

You know, the first time
you encounter these remains,

it's very emotional.

I have kids.

And you try to understand
why they do that.

There is...these two different...

..approaches to the Maya.

One of them is these
beautiful buildings,

the great astronomy
and science they develop,

and on the other side,
we have this blood-letting.

But this was part of
their cosmovision -

it was part of their religion.

It was part of their everyday life.

I wonder... If sacrifice was such
a big part of their culture,

especially with children...

But how often were they actually
doing that?

Cos I guess it would be
counterproductive

to be killing that many children.

I'm not trying to justify anything
but, you know,

I believe that sometimes
those were acts of love...

..to sacrifice children.

Remember that the Maya believe
in life after this life.

They were expecting this person to
either go to another place

and carry a message,
and they can bring it back...

So we don't know exactly,

but we do believe that
most of these sacrifices

or offerings occur in trying to
please the gods,

cos they were having problems
with drought.

When there's no rain,
there's no agriculture,

so there's no food production.

It's like, "Please send rain
to my people because we're dying."

It's been an unsettling introduction
to the world of the ancient Maya.

And how much more is still
out there?

I believe...I believe we will find
much more.

We're on our way to another
Mayan cave, one that isn't flooded.

It's a labyrinth of dry passageways,

thought to stretch many kilometres
beneath the jungle floor.

The cave is so vast,
it's not been fully surveyed

for the Maya secrets it may contain,

but getting into it
will be a challenge.

With our support,

Memo wants to explore a section
of the cave comprehensively.

We know that we have at least one,
possibly two descents on ropes,

so we're carrying as much rope
as we can,

plus all of our climbing
and ascending and descending gear.

I don't know exactly what
we're going to find inside

but, from what I understand,

this is one of the most remarkable
caves found anywhere in the planet,

and very few people have had
the privilege of going inside

and seeing what we're about to see.

This cave was so special
to the Maya,

they risked their lives to enter it.

We want to see just how far
they managed to get.

It won't be easy.

In the last few weeks,
someone fell to their death here.

We're taking every precaution.

Just so that everyone knows,

this is where the med kit
is going to be.

If it's me that ends up
incapacitated in there,

the med kit's here
and the stretcher's here.

Unless both you and I take
a catastrophic fall,

then we should be able to
come out and... Let someone know.

..raise the alarm. OK.

If you're not back by 6am,
we're coming in.

So is that 6am? Yeah.

Yeah, that's you.

Oh, it gets tight already.

It is.

Just go careful, mate.

Here, are we just passing bags
through? Yeah.

You definitely said no more caves,
Steve, a few years ago.

I know. I did...

Do you know what's amazing?

Just look at all this kit we've got,
and head torches and lights...

Imagine doing it naked.

Why would you want to do it naked?

The way they did -

barefooted with burning torches.

Shout me when you're through.

So we're only just into the cave,

and already we've got our first drop
down into the darkness.

It's uncertain how long it is.

How much are we sending down, Aldo?

Throw it all down that fall line.

See where... See right down through
that cleft?

Yeah.

Perfect, mate. Good shot. Good shot.

So when you're coming down,
don't run the rope over an edge

or somewhere that
it could get jammed.

It's so humid in here.

You can see all the water droplets
just floating around

in my headlight. Hey, Steve.

It's... Mainly, this is just
for support.

Pretty much on your feet
the whole way down.

Probably a 5m drop at the bottom.

Is the rope enough? Plenty.

I'm on the bottom level
of the first abseil.

Order of march, Steve.
Next, who do you want down?

I'm going to send Memo down next.

Yeah. Clear rope!

Are you OK, Memo?

I'm fine, thank you.

It's very slippery.

Yeah, yeah.

We're about an hour or so
into the cave.

Memo said the earliest people
were using this cave

was maybe 2,500 years ago,

so they would have been making
these descents that I'm doing now

on completely natural fibre ropes.

It's just incredible.

It actually makes us with
all our modern methods

feel a little bit pathetic.

We've got a long, long way to go.

It is hot.

It's taken us nearly an hour just to
get the team down this 5m drop.

If they came down to this on
a rope made from natural fibres,

how did they climb back up?

They may have had some kind of
scaffold system,

or maybe wooden ladders,

but we haven't seen
evidence of that.

After dropping down
this challenging overhang,

we come across our first sign
of the Maya.

Look at this, Steve.

What have you got?

This is a very important
symbolic construction

which represents the mountain of
creation. Yeah?

This is like a penis,

so this is a monument to life,
to fertility.

I don't know, but maybe we're
60 or 100m below the ground?

The Maya managed to come
all the way here,

build this fantastic altar,

made an offering,

and pray for rain or for harvest.

Wow. That's incredible. It is.

Although they referred to these
caves as The Place Of Fear,

the Maya were still drawn to them.

As their civilisation crumbled
and life became harder,

archaeologists think they ventured
into these labyrinths

to honour the gods
they held responsible.

We're four hours in.

We've reached a point
the passageway spreads out

like the spokes of a wheel, pointing
north, south, east and west.

So I think these caves run on
all the cardinal points, bizarrely.

Yeah. The one that we should be
going down is the west.

So that's... North is that way.
And that's west. Yeah.

Smashed pots litter the cave.

They once held offerings,

and the Maya are thought
to have broken them intentionally

to release the spiritual power
of what was inside them.

What's that?

Ground stone.

What?! That must weigh 25 kilos.

How did they get that down a cave?

That's amazing.

It's kind of like a detective story,
putting it all back together.

What have you got, Guillermo?

It's right here.

It's a beautiful, beautiful
ceramic pot.

First time I've seen something like
this. You've never seen this before?

No, and probably it's thousands
of years that had been there.

It's perfect. It's even sculpted.

It's perfect. It's beautiful.
It's unusual.

How on earth did they get in there?

They place it there -
they hide it.

The ancient Maya sometimes do that.
Whoa...

..and we can't even get it out.

Yeah. No. No way.

Yeah. It's stuck there.
It's stuck, yeah.

There are discoveries around
every corner here. Yes, of course.

Of course. We could spend
months inside this cave

and keep discovering things.

It's so cool.

Isn't that amazing?

Whoa.

Oh! Oh... Oh, wow!

Look at that!

That is one of
the most amazing things.

Look at it -
it's completely three-dimensional.

Amazing.

Well, it's definitely a mammal,
isn't it? 100%.

What were the important mammals
to them thousands of years ago?

Tapir? Pig, perhaps?
Could be a peccary.

It's so cool that they've taken
this chunk of rock,

this part of the cave, and they've
used its natural features

to form the head of the animal,
and the body as well.

You can see it almost looks like
it's leaping out the wall.

There's a parrot.

Look at that. That's amazing.

The face... That's so... It looks
like it was done by a graffiti...

It looks like it was done by Banksy.
Banksy.

THEY LAUGH

That's so good.

Imagine how far in we are
at the minute.

How long have we been going for?

Erm, six hours at this point.

Six hours.

So they came six hours into a cave
and created works of art.

The Maya believed some animals had
the power to enter the underworld,

and they celebrated them
in paintings like these.

Look at this, Steve.

It's a jaguar. It's a jaguar, yes.

I see it. Look at the face.
It's looking back over its shoulder.

Look at the eyes. It's amazing.

It's really amazing, the motion.
And I see the spots.

And look at the tail.
That's definitely a jaguar tail...

That's amazing. ..which makes it
different than the puma or cougar.

Yeah. It's really a jaguar.

It's beautiful.

Many of the oldest Maya deities
took the form of an animal,

and this was the jaguar god
of the underworld

known as the Night Sun.

The animal in front of it,
what's that?

It really looks like a deer.

These two animals were able
to go into the underworld

where we are right now...
Yeah.

..and be able to survive
and go back.

This painting represents
one of the most revered

and powerful Maya gods.

The artists overcame extreme dangers
to paint it here

in the deepest part of
this section of the cave.

Nothing here is done by
accident, is it?

Yeah, definitely nothing. Anything
that's done this far into the cave,

that's taken this much sweat
and effort. Yes, all this effort...

It's quite something to
think of someone

standing barefoot
where we are right now,

with a blazing torch to light them,

and painting, with charcoal,
this drawing onto the wall

and leaving it here, and now we're
sat here trying to decipher it,

trying to find its meaning.

It gives me goose bumps.

We are in the sanctum sanctorum
of religion of the ancient Maya,

the centre of the Earth -

the underworld.

Memo has given us a glimpse into
the incredible world of the Maya.

Their beliefs were so powerful
that they risked it all

to reach these subterranean places
of worship.

Everything about this place,

I just feel like I've been
connected back through time

2,000 years to the people that
used to walk through here. It's...

It's hard not to feel like that.
Yeah.

It's time to say goodbye
and move on,

but Memo's work in this cave
will continue.

Thank you, Guillermo.
No, thank you.

It was really a privilege to share
with you and your friends.

And not many people have seen it,
well, since the ancient Maya times.

Exactly, exactly,
thousands of years ago.

The Maya didn't only worship
the gods of the underworld -

they built pyramids to
the glory of the gods

that existed in the heavens, too.

Yucatan is incredibly flat,

so any time you find a hill,

it's not going to be natural.
It's artificial.

These blocks have been put here by
the ancient Maya

and would once have been
pyramids like that one there.

Over time they've crumbled,
and become part of the dense jungle

and home for its wildlife.

These limestone blocks
from the ruins are perfect

for animals to hide out in,

and this has obviously been the home
of a pretty substantial snake.

That's its shed skin,

and the live animal must be
at least 2m long.

No... Look at that.

HE GASPS

I'm watching one of the most macabre
sights in nature right now.

This is the world's largest species
of wasp, the tarantula hawk wasp,

which is as long as my thumb,

and it has a hold of a fully-grown
Mexican red rump tarantula.

The spider, though, is not
any longer putting up a fight

because it's been paralysed.

But this is not going to be
her meal.

This is a meal for her young.

Here she goes, she's going to
grab it again,

so she'll grab it in her jaws

and then start dragging it
to her burrow.

Once she's got it there,

she'll lay one single egg onto
the abdomen of the spider,

and that will hatch out and eat it
from the inside out,

eating around the vital organs
so the meat stays fresh

for as long as possible.

It's absolutely hideous. So macabre.

The Maya would have watched things
like this

and had significance for it,
because how could you not?

The wild world can be cruel,

and the Maya did gruesome things
themselves

to stave off nature's cruelty.

It didn't help them.

Famine, drought and other
natural disasters

could well have caused the collapse
of the cities of the ancient Maya.

We're back exploring the caves
under the Yucatan,

and my colleague Robbie Schmittner

now thinks he may have found
the perfect place.

He's been mapping underwater caves
in the region for years,

to help scientists protect
the fresh water there

from the growing threat of
pollution.

His search has identified
a cave in the forest

that's thought to have
Maya artefacts.

A lot of exploration is about
following stories and legends.

So, we have a lead that there is
a cave in the forest.

You never know -

I mean, it could turn into
nothing at all -

but it's still super, super
exciting.

The entrance has been explored,
but not its furthest reaches.

We want to see what's in there,

and find out how far the ancient
Maya journeyed into the cave.

Oh, cool. That's a proper cave.

It's a decent-sized entrance,
isn't it? It's massive.

A few metres in and we come across
our first signs of the Maya.

Check this out, Steve.

Whoa. That's an old altar.

That's amazing.

Look at that.

Wow. That's really cool.

And it has stucco,
plaster all over it.

Lime plaster like this
was used by the Maya from 600 BC.

When it was used on
buildings outside,

it often didn't survive the weather,

but in here, it's been protected.

Look at that.

It's like a face,
like a smiley face. Yeah.

That stalactite, that doesn't look
like it's been placed there,

I think the altar's been
built around it.

ALDO BLOWS RASPBERRIES

Mind blown.

Yeah. This is exactly what Memo
was talking about. Look at this.

This is THE most sacred thing.

A stalagmite coming up -

that represents the phallus,
that represents the male -

and this coming down,

the stalactite,
which represents the female.

This is probably why that altar
is right there,

because that is just screaming out

for everything from Mayan
iconography and symbolism.

It looks like it could have been,
perhaps,

something for carrying water in.
Yeah.

What is it? Pottery?
Yeah! Yeah, it's a bit of ceramic.

We didn't see anything like that
in that other cave.

I've never seen anything
like in the shape of that.

That's completely...unique.

I think you might have found
something quite special here,
Robbie.

It's a special place, definitely.

We're going to leave
the daylight zone here right now.

We need a bit more light.

We're going to push on as far
as we can into the cave,

going deeper than anyone has
explored before.

It's not just stalactites
coming down into the cave -

there are twisted tree roots
dropping down, searching for water.

And right there...is a whip spider.

Very creepy-looking critters.

That's absolutely stunning.

It taps around in the darkness,

with these extended legs
which function almost like antennae.

That's how it finds its prey.

It is genuinely quite worrying

when you think about how big
this cavern is,

how much weight is above it,

and how little support there
seems to be on the inside.

We're now hundreds of metres
from the surface.

There are no human artefacts
this far in,

but there are rock formations
and they're staggeringly beautiful.

This is probably the most decorated
cave system I've ever been in.

Everywhere you look,

there's something unique and new
and fragile.

And in this corner,

there are thousands of what are
called helictites.

It's where the stalactite
seems to go completely crazy

and starts growing off
in the wrong directions.

It's growing upwards,
it's growing sideways,

sticking out all over the place,

and it's still a bit of a mystery
why this happens.

The original idea was that it was
due to wind movement,

that the air would start the calcite
forming in different directions,

but I don't know, that seems
a little bit far-fetched.

Another suggestion is it could be
down to growth of bacteria

which just start going off in all
kinds of crazy directions, whatever.

All of a sudden, it transforms
these wonderful hanging structures

into something far more complex,

and every single one of them
is different and unique,

and just a little sound...

PERCUSSIVE NOTES CHIME

..like a subterranean xylophone.

We're deep inside the cave,

and there's no evidence the Maya
made it this far,

but something else catches our eye.

Whoa.

It's a lake.

Yeah.

A complete underground lake.
Crystal clear.

It's a thrilling discovery.

This is what Robbie lives for.

I think we should get the scuba gear
here and get in there and dive it.

Back there it looks all dark,
even with the light.

That's where I would start
searching first.

The dark shadow marks the start
of a water-filled cavern

that will either lead to a dead end

or continue on for countless
kilometres.

We decide to make camp
at the cave entrance,

and prepare to dive in the morning.

Cave diving is often described

as one of the most dangerous
types of exploration.

This will be one of the hardest
dives I've ever done,

and our lives will depend
on a single line.

I do need to prepare that guideline,

because when we measure the cave,

placing that guideline is our
lifeline to come back out,

but it's also the line which we need
to survey and make the cave map.

You can't get line knotted
at the market...supermarket already.

We have to do that all the time
before we go diving.

From Robbie's experience
of the geology in this area,

we're expecting to encounter
tight squeezes -

passageways barely big enough to
get our bodies through.

This will push me to the limit of
my diving abilities.

As far as my job is concerned
of being in charge of safety,

generally speaking,
on this expedition,

there is nothing,
absolutely nothing I can do.

As soon as they leave the surface,
they pretty much are on their own.

There is no rescue in there.

And the worst-case scenario
is...it's body recovery.

There is no half measures, really.

Yeah, it's pretty...pretty scary.

We don't know if it's a very easy
dive, what we're going to do.

We don't know what we'll find.
It's exploration, right?

My main concern is that
if I die tomorrow,

my last meal will have been
a Pot Noodle.

Nobody's going to die tomorrow.

Cheers to that.
Cheers to the dive. Cheers.

Cheers to that -

safe dive, safe journey
and safe return.

Goodnight, everyone. Sleep good.

Night-night. Night, dude.

So, one side is the jungle
and the other is the cave,

and somewhere deep in there...

..is probably the thing I'm most
frightened of in the whole world.

Never been much good at...little
narrow spaces and squeezes.

Get us coffee, Aldo. Hmm...

How did you sleep?

Yeah, very well.

I sleep better in a hammock
than I do in a bed.

I love living like a caveman.

The simplicity of life...

Get up, start fire, have coffee.

I don't know if cavemen had coffee.

What?! OK, I don't want to be
a caveman any more. Nah.

Robbie, do you want coffee?
Sure.

How do you take it?

Milk, please.

Dive plan for this morning, Robbie?

Our main danger always, always
in cave-diving is our own mind.

The most important thing is
stay calm at all times.

We cannot panic.
It's impossible. Not...

Not an option, right?

This is subtly different,
what we're doing this time.

We're going for a slightly
different system.

I'm not using the full facemask
that allows me to talk underwater.

Instead, I'm going for a more
conventional cave diving set-up,

which should be safer,
more manoeuvrable

and help me to get to places

that I just wouldn't be able to
with the big mask.

I'll go in front with the reel.

You know, stay close by
the guideline -

always in reach distance.

If anything goes wrong,
if anything is not ideal,

let's just call it and go back.

All right, sounds good.

All right. Let's do it.

1400 hours.

OK.

All right. Waiting on you, Robbie.
All right, let's do this.

We're the first people ever
to see these stalactites...

..and set our eyes on this.

This is an optical illusion
caused when a shallow pocket of air

is trapped against the roof
of the cave.

I don't know if the air
in here is breathable.

It probably, actually,

from the fact my breathing is almost
instantly going up quite a lot...

..probably means that
there's not a lot of oxygen in here

and it's mostly carbon dioxide.

Oh, yeah. The air in here is not
good. Definitely not.

HE BREATHES IN FROM OXYGEN CANISTER

There's always that
slight sense of panic

as his heart rate starts going up,
and your breathing starts going up,

because there's just not
enough oxygen.

HE BREATHES IN FROM OXYGEN CANISTER

Robbie has just dropped down into
a little crack and he's disappeared,

and he's gone completely,

which is pretty nerve-racking,

because it means that
I'll have to follow.

But this little bell here,

nobody's ever been here before.

And where Robbie's gone now,

I'm not sure anyone should ever go,
really.

Here, the cave drops down into
a tight squeeze -

the smallest I've attempted.

HE SCREAMS

I can't move forward or backward.

I'm stuck.

HE SCREAMS

I force myself to slow down, calm
down and think about my breathing.

I exhale, and the cave lets me go.

Robbie's waiting on the other
side in a clear tunnel.

My only comfort is that I'm with
one of the world's top cave divers.

He stays alive because he dives
within his ability.

If he reaches his limit,

he always turns back and lives
to dive another day.

We're approaching a second squeeze
and I'm nervous.

This one is technically
more difficult than the last,

but I'm determined to try.

Something on my harness is caught.

I'm through to the other side,

but now further away from safety
than I've ever been.

Beyond here, I can see another
squeeze and it's smaller still.

I don't think there's any way
I can physically get through there.

This could be the decision
of my life.

Robbie will continue on mapping,
while I turn back to safety.

Wow. Wow.

Oh...

What an experience.

But we all want to know how much
further Robbie managed to go.

You ran out of line?

What happened, man?

It keeps going and going.
It does?

Yeah, you've got to see on here.
It got really tight.

Watching Robbie's helmet cam footage

shows exactly what he had to go
through to put all of his line out.

He reaches a squeeze so small,

he has to carry out the most complex
manoeuvre in cave diving.

He removes both his air cylinders,
passing them one by one

through the tiny restriction
into the darkness below,

connected only by a length of hose
and his mouthpiece.

His reward is a seemingly endless
passageway on the other side.

I just pushed on and on
and at one point it was,

"Oops, no more line."

And the cave keeps going.

To carry on without line

would be breaking the golden rule of
underwater cave exploration.

How much line do you have on here?

It's about 500m.
Half a kilometre?!

Half a kilometre. We've gone
half a kilometre into the cave...

..and that's nothing,
it hasn't even... Wow.

It keeps going. Wow.

That's amazing news.

Everything I'd done up to that point
was the maximum that I'm capable of.

Being given the honour of
being taken into that place,

it's Robbie's incredible experience
and knowledge

that's allowed that to happen,
and for that I owe him big time.

It's been an incredible journey.

The information being gathered
by scientists

will help prevent further pollution

of these vast and interconnected
waterways.

During our six-week expedition,

we've explored and mapped
deep underground,

adding to the growing knowledge
of both the Maya

and the area's precious
water resource.

The thing that sets us apart
as a species, as human beings,

is our desire to explore,
to discover, to solve puzzles,

and to expand the limits of
human knowledge.

Something led to the downfall
of the ancient Maya.

One theory is that overdevelopment
caused an environmental crisis

which saw them run out of
fresh water.

In Yucatan today,
there's another freshwater crisis

through pollution caused
by over development.

Surely, we should be learning
the lessons.