Original subtitles

A toxic facility in the British countryside off the beaten track.

They're far from any urban centre workforce.

They're making something so dangerous,

they want it far away from other people.

A deceptively alluring ruin in Malta.

Nobody wanted to be here,

and there was always the risk that you'd never make it out alive.

A Ukrainian city littered with strange concrete remains.

It was top-secret.

Even saying the word 'tunnel'

would be enough to get you sent to the gulag.

And the site of a biblical disaster in the valleys of Pennsylvania.

The local mill owner started to say that this was never going to fail,

and he was lying through his teeth.

Decaying relics, ruins of lost worlds...

..Sites haunted by the past...

..Their secrets waiting to be revealed.

In north wales are the remains of a secret facility now a wasteland.

This is a wild place,

and it is far from civilisation.

The surviving signage suggests a dirty history.

North wales is a mining area of Great Britain, but there's

nothing of the infrastructure of mining about this place.

Would make no sense to put a factory here without workers nearby,

so this seems to have some classified, official purpose.

Hollowed-out buildings in a remote location

point to a history that's been erased.

So, you look inside these buildings and it's very, you know,

sort of bare, austere.

Concrete walls clearly intended to store something

or make something that was combustible, sensitive, fragile.

You don't see remnants of wallpaper.

This place has been emptied systematically

and scrubbed from top to bottom.

And there's this kind of lunatic graffiti all over

the walls of one of the structures.

Messages from the long-departed

tease a deeper history hidden beneath the surface.

If I know anything about the archaeology of the abandoned,

I know that what's important here is not these buildings.

What's important here is what lies beneath.

Colin barber first came here ten years ago.

'Tis a beautiful place.

I think it reminds us of how bad things could be,

and thank goodness we never used what was produced here.

In one building he found strange writing on the walls.

Well, I thought it was a graffiti,

but it's mixed up with personal comments

and comments upon the general state of the world at that time.

And as we look at it more carefully,

I mean, i'm not great at math but these

are clearly mathematical equations, formula of a very advanced nature.

Well, this here is magnesium carbonate.

The one below that is sodium chromate.

This might have had some military lineage because,

you know, classification was so strict.

They would tell scientists often,

"you can't write these things down on paper

'cause the paper could go astray.

We'll write it on the wall. We can police up the walls.

We can't police up every scrap of paper and wastebasket."

Secrecy was Paramount,

because here they were working on a deadly chemical - mustard gas.

Used in the first world war to clear out enemy trenches,

this weapon was a toxic sulphur compound.

Mustard gas has nothing to do with mustard and it's not a gas.

It is sprayed into the air as a mist.

And if you get it on your skin,

or god forbid you get it in your lungs,

it causes blisters wherever it goes -

blisters, burning and pain.

Mustard gas killed 90,000 soldiers in the first world war.

This was the beginning of large-scale chemical warfare.

Mustard gas was definitely one of the most horrific weapons

of the first world war - so horrific that people talked about

banning its use after the war.

But they were also viewed by the government in the 1930s

as an essential part of British deterrence, so they manufactured

a lot of mustard gas in the interwar period to be prepared

in case they needed it in world war ii.

Well, they built these tunnels because in 1939,

when the first factory came online, they were producing

216 tonnes a week and they only had storage for 100 tonnes.

At the onset of world war ii,

the government dug new depots underground,

safe from German bombing.

The largest was here at the ms factory.

In these tunnels, mainly it was storage.

65-tonne tanks were bought in and eventually you could store

4,000 tonnes in here.

This facility was so well hidden and so secret

that throughout the whole war the Nazis never knew it was here.

Facilities like the ms factory

made enough mustard gas to be used in another chemical war,

but one building on the site had an even deadlier purpose.

This is building p6.

This place was built to manufacture pyro mustard gas.

It transpired that, with improvements in technique,

they didn't need this particular building to do that.

Bred down here both sides were the offices of all of

the scientists, the chemists.

Nobody could come into here unless they passed the guard.

Here they began work on a new weapon that would be infinitely more lethal.

You think mustard gas is dangerous.

Building p6 is a facility for making u-235,

enriched uranium -

the stuff you use to build atom bombs.

Behind the scenes during the second world war,

scientists on both sides were in a race

to build a thermonuclear warhead.

Whoever could build the atom bomb first would likely win the war.

But both sides were missing a key ingredient.

At the beginning of the second world war

we were looking at a way to remove

the isotope uranium-235 from uranium-238,

because this substance was essential in the manufacture

of any atomic bombs.

That was the bit that made you go 'bang'.

To make that bang they needed nearly 15kg of radioactive material,

an impossible-sounding task.

But here in building p6 they tested a new process.

By heating uranium and putting it through a filter,

it would become enriched.

It was a discovery that transformed nuclear science.

Here in north wales

the allies achieve something that no-one had ever achieved before.

They're able to produce enriched uranium with u-235

on an industrial scale.

In less than four years the Manhattan project tested

its first nuclear bomb, and a month later two were dropped on Japan.

The second world war ended with a chilling glimpse of the future.

Nuclear weapons ended the second world war quickly, and if

it'd been necessary they'd have been used to end the war in Europe too.

At the close of the second world war,

the ms factory was decommissioned and its materials were disposed of.

Everybody now appreciates the importance

of the use of the atomic bombs.

It is the thing which has defined our lives,

and to think that it's happened here in a little Welsh village,

I think most of 'em were very impressed with that.

On the island of Malta,

in the calm waters surrounding the capital valetta,

lies a marooned site with hidden depths.

This building sits right on the waterfront,

catching the sunshine.

And in many ways it looks like an idyllic place to be.

But parts of it are in real disrepair.

It's overgrown in places,

and on the stairs this creeping plant has taken over.

The balconies look like they could collapse at any minute.

The walls here are covered in

carvings, names, dates, pictures.

There's hundreds of years of history etched into the stone.

As inviting as it may have first appeared,

the true nature of the site is obscured.

Those rooms upstairs are light and breezy.

It feels like it had an air of luxury about it back in the day.

It looks like it could be a palace or a rich person's home,

but it's something far, far different.

On the surface, this place seems to have been one thing for most of

its life, but if you then take a walk behind the staircase,

something surprising creeps up on you.

Carved from the rock behind is an entrance to an underworld.

Some of these tunnels are very small, very claustrophobic,

and the further you go in, you get to these dungeon-like spaces

and these rooms full of rusting equipment.

You start to wonder what was really going on here.

Travelling from afar, the first arrivals to this mediterranean site

landed here in 1643.

They found themselves lined up outside the doors

of the main building, later referred to as the old palace.

Alex torpiano is an architect who worked for the firm that manages it.

This is the courtyard of the oldest palace of the complex.

People would arrive from the ships through this entrance.

Their goods would be taken to the two warehouses

on either side or at the back,

and they would go up this grand staircase to their living quarters.

Once you're bought into here, there's no way you can get out of

this place before a set period of time is over.

The elaborate design with its grand courtyards,

large rooms and breathtaking views

immediately makes clear this was no ordinary prison.

The people staying here weren't necessarily the kind

that you would normally lock up.

There had to be a reason why they were being isolated,

even in these relatively nice conditions.

This is the first floor of the 17th century building.

These are the accommodation,

the living quarters of the people confined in this building.

Nice, airy, high ceilings,

well ventilated, well lit.

Not a poor place to be confined.

But despite the visitors' wealth and status, the locals still had

reason to fear them and locked them inside under armed guard.

The people who were confined here were not confined because they were

criminals but because they were travelling to Malta from other

countries in the mediterranean, and they needed to be isolated

from the population just to make sure that they didn't

carry diseases and wouldn't spread and affect the population.

This is the lazzaretto,

Malta's first line of defence against plague and pestilence.

We've seen recently just how quickly infection can spread.

Even in the modern world it's extremely difficult,

if not impossible, to control an outbreak.

Back then people didn't even know that cleanliness

helped keep you safe.

The only measure they knew about was to quarantine people,

to isolate them from the rest of the population.

You quarantine the people upstairs

and you quarantine the goods downstairs.

Throughout the middle ages, a number of outbreaks of disease at ports

led to deadly pandemics sweeping across Europe and beyond.

The worst of these, the black death,

had struck three centuries before this place was built.

It killed as many as 75 million people across the world.

The island itself had been used as a quarantine site

for more than 100 years before they built this structure.

But they needed something a bit more secure as time went on,

and that's why they started to build this facility.

One of the reasons this place is so large is, once you were there,

the quarantine, the isolation was absolutely unbreakable.

Derived from the Italian word for the number 40,

a quarantine typically lasted 40 days -

enough time to see if any symptoms appeared.

People didn't really understand what caused infections and how

it spread, but I think fairly early on they decided

that perhaps the best thing to do is to isolate whoever was sick.

Quarantine was slightly different in the sense that people who are not -

or you didn't know that they were sick, they could be sick,

so they were kept in a period to see whether the signs

of the plague would come out within that 40-day period.

There were guards that making sure that people did not go in or out.

Effectively death penalty if you broke that rule.

No matter your status or level of wealth,

enduring the isolation period was par for the course

for all those wishing to set foot in Malta.

If you had 40 days to kill, this wasn't the worst place to be.

I mean, you had the views and the sunshine,

you had plenty of company.

It's almost like a holiday retreat

but with the hazard of a potentially deadly disease.

Many centuries worth of visitors were locked inside here,

and their presence is still evident.

What's amazing about this place, though, is that its history is

carved into the walls of the building, literally.

On either side of the living areas there were these terraces,

which the people could use to while away the time

with the view of the sea and of valetta and the sun,

and many of them left a Mark on the walls.

Among the countless numbers quarantined here

was a famous novelist, a future prime minister of the United Kingdom

and the scandalous romantic poet lord Byron.

Here we have what is attributed to be lord Byron's graffiti

when he was here.

Difficult to read but experts tell us that that is what it is.

The graffiti Mark the history of the people who came here,

and some of them wrote their story.

There's one who talks about coming from constantinople,

the other one etched the ship that he was on.

Me, it's four beautiful walls which contain all these stories

which need to be deciphered.

But away from the sunshine and sea views

lurks a far darker secret.

What about these other areas - not the nice areas

for holding wealthy travellers but these darker areas,

the more claustrophobic ones, the hidden spaces?

If the people were being locked up in the nice part of this site,

then what exactly was going on back there?

The lazzaretto was repurposed

to guard Malta against a very different threat.

Now, the island had been important for centuries

'cause it's at a strategic position in the mediterranean,

but in world war ii it became even more important.

So this was a nerve centre of operations of submarines

in the mediterranean with the royal Navy for the allies,

so this was a very important place.

In 1940 Italy joined forces with Nazi Germany, and soon

the axis powers will dominate more than just the mediterranean waters.

Malta under British rule was to become a Thorn in the enemy's side,

and the lazzaretto itself was drawn into battle.

So this is the heart of the submarine depot.

A submarine depot means basically two things -

one is the control of operations,

so it's a communications centre for submarines, and the second,

you were supposed to have somewhere where submarines could refuel

from the oil tanks that were stored underground as well.

This place was all about repairing and refuelling the submarines,

getting them ready to be sent back out on patrol in the mediterranean.

The two sides used submarines very extensively to attack

especially supply ships and also, of course, the battleships.

The battle of the submarines in the mediterranean, I think,

was crucial in the way the war developed.

The above-ground buildings were requisitioned for operations,

but on their own they weren't enough.

If the allies are gonna use this as a staging point, that's also going

to make Malta one big target.

If you're gonna put facilities here,

they have to be facilities that can withstand a heavy bombardment.

During the war, Malta suffered 3,343 air raids.

Use of this underground complex allowed work to continue here

despite the bombs,

but the full picture of how it all ran is still hard to piece together.

The whole system of these rooms,

these chambers, partly to contain equipment and power supply

and also to have habitation for the soldiers, for the Garrison.

Difficult to understand exactly what the purpose each room was,

because first of all we don't find that much documentation.

Presumably all of this was secret.

Suppose somewhere there is an explanation.

From here allied submarines went out in to the sea

and caused untold amount of damage to the German and Italian navies

and their supplies.

This island was absolutely crucial

in winning the war in the mediterranean,

and this place played a key role in it.

Despite the war damage, the site was

used as an infectious diseases hospital for the next 30 years.

But once vacated, neglect, vandalism and time each had their way with it.

Today the stunning architecture on display here is now the focus of a

major restoration project

hoping to return the buildings to their former glory.

It's a unique building, and it should find its place again

in the glory in the middle of this harbour.

I think it's a place where we could learn the very complicated history

of this place, which reflects the history of the island.

In rural Pennsylvania lies a forest valley and a trail of destruction.

Across the valley you can see these jagged structures -

very well weathered, torn apart.

Whatever somebody did here was some mass industrial process,

somewhere in the back woods of the allegheny mountains of Pennsylvania.

They're almost completely subsumed by mother nature.

They're overgrown.

They've been clearly there for some time

and not been used for a long while.

Following the trail north is another piece of the puzzle -

the remains of a wall.

They were once in some sort of line,

but they're misaligned and almost like a sort of dominos in -

that have fallen in funny shapes.

It could be one of the hundreds of dams that we see in the runs

and streams of Pennsylvania.

But if this was a dam,

what smashed it to pieces?

At the bottom of the valley is the quiet town of Austin,

but it wasn't always this way.

Alvie fourness grew up a few miles from here.

110 years ago this town had a population of about 3,000 people.

This would have been a very busy town, all types of businesses here.

There would be schools and hospitals,

a movie theatres, restaurants.

Back in the early 1900s, Austin was a boom town.

Like many prosperous settlements,

there were opportunities here for a few less respectable enterprises.

One of our most famous citizens at the time was Cora Brooks,

who had a boarding house located about 2 miles north of here -

a brothel sort of environment probably, although those type

of things were very illegal.

Cora was somewhat an outcast in the community.

But while Cora Brooks' establishment was frowned upon by many,

in time she would become a sort of saviour of the town.

First, though, Austin had to weather another storm

that threatened to make this boom town go bust.

I mean, this region was famous for its trees,

and so the lumber market was a big thing.

But soon enough, too many people working,

the place was effectively deforested,

and the bottom had fallen out of the lumber market.

But one entrepreneur found a way to make money.

His name was George bayless,

and here he built the bayless paper mill.

Bayless's paper mill was a huge, huge complex.

It took the raw material, all the wood, turned it into pulp,

cleaned it, dried it and then made it into paper.

A massive operation

with specialised buildings spreading out across the valley.

The pulp product would come into this area,

be placed in these digestors or vats.

Certain chemical processes were occurring,

give the final pulp product.

The mill produced almost 500 tonnes of paper a week.

But something on this scale needs reliable, cheap power source.

1900, water is the key to that.

To power the mill, bayless commissioned this - the Austin dam.

The first dam was just an earth-built one,

and that absolutely worked, and it showed what could be achieved.

And then of course the factory got bigger,

the demand for power got bigger,

and you're gonna need a bigger reservoir,

and a bigger dam to hold it back.

To upscale the enterprise,

the factory owner hired an engineer to draw up a design.

It was gonna take 43,000 cubic feet of concrete

and a dam that was 50 feet high.

This was gonna be an epic engineering feat,

but it was also gonna be expensive.

Bayless commissioned the biggest gravity dam in Pennsylvania.

A clear problem building a dam in any valley, and particularly

in these types of valleys, where you've got vegetation and a soil,

is the problem of the soil being eroded in and around the valley.

The gravity dam relies on weight.

32,000 tonnes of concrete resisted the push of the water,

but underneath was ordinary soil,

which water could pass right through.

I mean, if you think about it, if you build a swimming pool at home,

you don't just dig a hole in the ground and pour water in,

because it'll seep through.

And that's kinda like the problem they've got here,

but it's on a much bigger scale.

If water can get underneath, gravity wouldn't be enough to

hold back the reservoir and the dam would fail.

So the engineer designed a safety mechanism -

an underground wall to prevent water getting under the dam.

In December 1909,

the Austin dam was completed but something wasn't right.

It became obvious early on that the dam would be troublesome.

Water was seeping up out of the ground,

and also there was cracks developing in the structure itself.

The townsfolk had called it the dam that could not break,

but fate would prove them wrong on the worst possible day.

September 30, 1911, is the key date.

The town was celebrating polling day. Everybody was out.

It was very, very busy.

A week of rainstorms bought unprecedented amounts of water

into the valley.

The reservoir at that point was really high as well,

just 2 foot below the overspill level.

That's incredibly full.

And at that point catastrophe happened.

The structure over here moved more or less like a door.

It swung open and allowed the water to start gushing out.

The wall behind me also slid about 50 feet.

A torrent of water came crashing down the valley,

destroying everything in its path.

When the water came gushing down the valley,

the first thing it hit was the paper mill.

It came crashing through, destroying,

entering almost every room.

And it gathered up everything in its path,

including all the raw material, all the tree trunks,

and then it headed downstream towards the town of Austin.

The east side of the town got hit worst due to the slope

of the valley, pushed the wave more in that direction.

And the scene was of almost sheer devastation.

Almost every building was submerged.

You could just see the steeple of the church.

That was the only thing

that you would have recognised that there was a town there.

In 15 minutes the town turned from celebration to disaster area.

Almost no-one saw it coming.

Bayless was determined to get his new, expanded paper mill

up and working, and if that meant he had to cut a corner,

that's what he did.

The underground wall designed to protect the dam

was deemed too expensive.

Bayless ordered the engineer to scrap it,

turning it in to a ticking time bomb.

The dam is built on the cheap.

It's built to take the minimum amount of money

to hold back the maximum amount of water.

The local mill owner started to say that this is a dam

that was never going to fail, and he was lying through his teeth.

3,000 residents were in the town when the water hit,

but the people of Austin had an unlikely guardian angel.

Luckily the alarm had been raised by, of all people, Cara Brooks.

The outcast brothel owner saw the flood coming

and she warned the town, saving thousands of lives.

The phone call allowed the people of Austin 15 minutes' warning.

And the town below,

out of that town of 3,000 only 78 die in the disaster.

The history of that flood is preserved in the Austin

dam memorial park.

In the early 20th century, anybody could build a dam in Pennsylvania.

There was no regulation, there was no inspection, and that was

what led to a poorly designed dam smashing the very people,

the very town it had been designed to power.

A tragedy like the Austin dam,

like many sort of tragedies that involve humans,

is there's often a mistake that's made or a decision that's made

that ends up leading to something

that you didn't necessarily predict was going to happen.

And that's exactly the case in Austin.

Just cutting a few corners,

or not doing the right engineering mitigation

to stop something like this happening,

ultimately led to the destruction of the dam

and to the loss of life.

Today construction is held to a strict engineering code,

perhaps the greatest legacy of the Austin dam disaster.

In Ukraine's capital city, Kiev,

a concrete monolith stands at odds with its surroundings.

As you wander around Kiev, you can start to see some strange things.

I mean, there's this one example - can only be described

as like a submarine in a park.

You can actually walk inside of it

and then you can see how truly enormous it is.

It's 50m long, 15m across.

The walls are incredibly thick.

My first thought is it's gotta be a typical example of,

you know, eastern European Soviet-era kitsch,

but then on the other hand,

if it was kitsch, it would prettier, you know, it would be painted up,

it would look more like a submarine.

It must have been built where it is.

It must have been built for a purpose, but what could that be?

This object sits on the bank of the dnieper,

the largest river in Ukraine.

The dnieper is a big, slow-moving, shallow river, swampy in spots,

and divides the city of Kiev almost right down the middle.

A larger piece of the puzzle sits on those swamps.

You can see this weird, kind of snake-like concrete construction,

which seems to be sinking down into a swamp. What's that for?

Two sites 11 miles apart are both clues to one of

the greatest engineering secrets behind the iron curtain.

Local historian valery lysenko

has been coming to Kiev's natalka park since he was a child.

Translation: Back then you couldn't even ask about it.

What was a state secret half a century ago is now being uncovered.

The locals gave it many names. Some call it a train.

Some call it a submarine. The most accurate name would be a caisson.

But not many people understand what the word means.

The story here begins 80 years ago

with the river that runs through the city.

Across this river you have eight Bridges, and as you can imagine,

these are essential for keeping goods and people

moving back and forth across the river.

But 80 years ago they were recognised as a huge problem.

In 1920, Kiev faced an invasion.

The Poles attacked and took over Ukraine and captured Kiev.

The red army drove them out after just a few weeks,

but it made Lenin and the other Soviet leaders

realise how vulnerable this area was.

Translation: What did the Polish army do before the retreat?

The obvious thing - they destroyed all the Bridges,

the large ones across the dnieper.

Kiev's Bridges were rebuilt,

but the battle taught them a valuable lesson for the future.

One thing they'd learned is that Bridges were very vulnerable.

What if an enemy air force came in and knocked out these eight Bridges?

They would be helpless.

There'd be no way to get supplies or troops

back and forth across the river.

They needed a better system.

To protect the city, the Soviets began work on a secret weapon.

Translation: There are many local legends that surround this place.

Some say that there's a train hidden inside the tunnel.

Others claim that the water doesn't freeze inside the tunnel

because of the radioactivity.

The official name of this structure was object 1,

but to the people of Kiev it goes by a different name.

Translation: People call this place Stalin's subway.

Kiev had learned the hard way

that if an enemy destroyed its Bridges there was no way to get

supplies across the dnieper.

So here in the swamp they began digging a tunnel

that would run underneath the river.

They're gonna be railway tunnels, but they're gonna have steel plates

that can be lowered into place over the railway tracks to accommodate

vehicle traffic as well.

Around 1938, construction started in secret.

Translation: The Soviet union was obsessed with secrecy.

They liked to hide everything.

Stalin decrees that if any of these 2,000, 5,000,

10,000, eventually 12,000 workers enlisted in these sites

ever even breath the word 'tunnel' they'll get ten years in the gulag.

But digging from one side of the river to the other was too slow.

In the 1930s, Europe was on the brink of another world war.

Kiev faced invasion again.

To speed up the dig they used caissons.

80 years ago this park was a wetland.

The caisson was constructed on the surface.

And then they would use high-pressure hoses

to remove the soft sediment beneath,

thus sinking that tunnel into the ground beneath the river.

A column of concrete rings would be built,

creating a pressurised chamber

in which the engineers could beginning digging in both directions.

Translation: And so this tube,

when it was lowered to the relevant depth,

they constructed the so-called manual tunnel-boring machine.

Now it's done mechanically, but back then it was done manually.

It was a metallic construction which allowed them to move forwards.

The Soviets hoped this would turbocharge the dig,

but by August 1941 they had run out of time.

The enemy was at the gates.

Believing they could hold off the German army,

Soviet top brass ordered the workers to keep digging,

but the Nazi force was overwhelming

and Kiev's Bridges were destroyed again.

They branched south to try to take Kiev,

'cause it's such a big prize and it's such a big population.

And they bagged 650,000 red army troops -

one of the greatest military victories of all time.

When Kiev fell, work on the tunnels finally stopped.

It's believed that maybe they got 10% of it done

before the war intervened and they had to stop.

Translation: They were afraid to talk about it even years after.

There is a high possibility that all the prisoners who worked here

were later exterminated.

Attempts were made to restart the construction, but in 1949

the tunnels were abandoned and the project covered up.

Translation: Many years after the war, the subway was built in Kiev.

When this area was no longer restricted for the people and

they were curious as to what it was,

only then the newspapers started writing about it openly.

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