Original subtitles

[deep rumble]

[soft music]

- [Danny] Mysteries can be buried anywhere,

under the earth,

[volcano exploding]

[airplane engine revving]

beneath the sea,

[plane engine roaring]

or even right under our own feet.

[coins clink]

And when we stumble upon them,

sometimes what we find can change history.

[soft music]

Tonight, puzzling discoveries

that lead to more questions than answers.

From a top secret message in an unlikely place-

- They find words like sword and Juno.

These are code names for Normandy landing sites.

- To MI5, this is no longer a coincidence,

it's a crisis.

- [Danny] to a mysterious metal object-

- His heart is racing.

He knows something about this has to be important.

- [Danny] to a strange underwater signal.

- SOSUS is top secret.

Sharing what he's figured out

would risk exposing this classified government program.

[audio system buzzing]

- Join us now,

because nothing stays hidden forever.

Most of us don't give spare change a second thought.

We toss it in a jar and move on.

But for one New Yorker,

a few cents cracked open a vault of Cold War secrets.

- It's June of 1953,

and a 14-year-old news boy named Jimmy Bozart

is leaving a Brooklyn apartment building.

It's collection day, so his pockets are heavy with coins.

- He knows that one of his regular stops,

a pair of school teachers, always give him a tip.

They give him 50 cents

on a 35 cent subscription to the Brooklyn Eagle.

- He finds a quiet corner to go through the day's take,

and as he's sifting through the coins,

he drops a nickel on the stairs.

- [Danny] That's when something extraordinary happens.

- The coin splits clean in half,

like opening an Oreo,

except instead of cream filling, the coin is hollow.

And inside, there's a tiny piece of micro film.

- [Martin] Jimmy brings the coin and the film home

and holds the film up to the lamp in the living room.

Only this film, it doesn't include a photograph,

it doesn't show a person, a place, or a thing.

Instead, it's just columns of numbers

in eight and 10 digits.

- [Andrew] To most people, these would be random numbers,

but Jimmy has read his sheriff spy comics,

so he knows what this really is,

a secret code.

- [John] He shows his dad,

who tells him to take the film and the nickel to the police.

So, the next day,

Jimmy brings the strange nickel to his friend,

whose father is an NYPD officer.

- [Danny] The officer can tell

this isn't just pocket change,

so he contacts federal agents to investigate further.

- [Andrew] Federal agents take one look

and realize that this is a precision-built device

meant to convey secret messages to spies.

- [Martin] The most impressive part about this

is that it's not one nickel

that has been split down the middle,

it's two separate nickels that have been composited together

to make this piece of spycraft.

- [Andrew] There's even a tiny pinhole

in the letter R of "TRUST,"

which opens a secret latch.

- [Danny] The engineering is impressive,

but the real mystery is the message inside.

- [Andrew] The FBI's top code breakers can't crack this.

They pass it along to the CIA,

but that agency is still in its infancy

and doesn't have the

sophistication to break this code.

- [Danny] For four years,

the CIA can't make sense of the message,

until 1957,

when an unexpected lead blows the case wide open.

- [Martin] A man walks into the US embassy in Paris

looking haggard and anxious.

He identifies himself as being a Soviet intelligence officer

and announces his intention to defect to the United States.

- [John] His name is Reino Hayhanen.

He's a low-performing KGB agent

who's been summoned back to Moscow,

and he's convinced that this means he's about to be killed.

So instead of following orders,

he decides to switch sides and work for the Americans.

- [Andrew] He's eventually interrogated by FBI agents

who begin showing of different pieces of evidence,

including a photograph of the hollow nickel.

- [Alex] Hayhanen not only confirms that the coin was

Soviet, but he gives the FBI the key to decipher the code.

- [Danny] In a stunning final twist,

it turns out the message in the nickel

was meant for Hayhanen himself.

- [John] The code is a set of instructions

for him to start up life in America.

Meeting locations, dead drops sites, contact protocols.

It's everything a freshly deployed Soviet spy would need.

- [Martin] It seems like the kind of crazy coincidence

that would be featured in a movie,

and eventually that's what it became.

Decades later, the story of the hollow nickel

becomes a part of Steven Spielberg's movie

"Bridge of Spies."

- [Andrew] In the end, this Cold War mystery

wasn't solved thanks to advanced espionage techniques,

but really instead thanks to a paperboy

counting change on a step in Brooklyn.

- [Danny] That wasn't the only surprising place

secrets turned up.

In wartime Britain, a different puzzle

almost unraveled a mission far bigger.

- [Don] It's 1942, and World War II is raging throughout Europe.

As bombs fall across London,

a British intelligence officer

tries to find a moment of peace with his morning ritual,

the crossword puzzle in The Telegraph.

- [Kavitha] He sits down with a hot cup of tea

and reads the first clue, French port.

He knows the answer, Dieppe, and starts to write it in.

- [Danny] Then his hand freezes

as a chill runs down his spine.

- [Don] Dieppe is more than a French port.

It's the name of the French town

where, in just two days,

Allied forces planned to launch a secret amphibious raid.

The invasion is meant to test the Allies' ability

to take back a small piece of France and boost morale.

- [John] This town being in the crossword puzzle is weird,

but he figures it's just a coincidence

and goes on with his day.

Two days later, the raid proceeds as planned.

[artillery fires]

However, instead of becoming a morale boost,

it's a massacre.

- [Austin] Of the 6,000 Allied troops that land that morning,

nearly 60% are killed, wounded, or captured.

The survivors retreat,

and everyone else is taken by the Germans.

The Allied commanders can't shake the feeling

that the Germans were waiting for them.

- [Danny] To figure out what went wrong,

MI5 is brought in to investigate.

- [Don] That's when one of the intelligence officers

remembers that crossword puzzle.

- [Kavitha] They tracked down the puzzle's creator,

a man named Leonard Sydney Dawe.

Dawe is a respected headmaster at a local school,

a World War I veteran.

By all accounts, a modeled British citizen.

- [Austin] After a thorough investigation,

MI5 determines no signs of espionage.

This was just an unfortunate coincidence.

- [Danny] Almost two years later, it happens again.

And this time, the stakes are much higher.

- [Don] In May of 1944, the Allies are preparing

for what is the largest amphibious assault

in military history, Operation Overlord,

the D-Day invasion

that could crack open Hitler's Fortress Europe

and change the course of the war.

- [John] Over the next several days,

MI5 personnel once again

find a series of strange crossword puzzle answers

in The Telegraph.

Words like sword, Juno, and gold.

All of these are top secret code names

for Normandy landing sites.

- [Kavitha] Then even more code words show up.

Utah, Mulberry, Omaha.

- [Danny] Finally, the most alarming of all, Overlord,

the classified code name

for the entire D-Day operation.

[artillery fires]

- [Don] To MI5, this is no longer a coincidence,

it's a crisis.

They storm into puzzle writer Dawe's classroom.

He is escorted out in front of his stunned students.

Within hours, he's interrogated,

accused of being a German spy.

- [Austin] Dawe is baffled.

He maintains he's innocent.

He claims that he doesn't even choose

the words of his crossword puzzle.

He enlists the help of his teenage students

to give the words, and then he creates the clue.

- [John] As D-Day approaches, he maintains his story,

but MI5 keeps him in custody, anxiously waiting for updates.

- [Danny] If the Germans are tipped off,

Dawe will be tried as a traitor.

- [Kavitha] Fortunately, this time, the invasion succeeds,

and the Germans are caught completely off guard.

- [Danny] With no evidence linking the puzzle to a leak,

MI5 has to let Dawe go.

But decades later,

an unexpected confession finally sets the record straight.

- [Don] In the 1980s, some of Dawe's students come forward.

They explain that in the weeks before D-Day,

their small English town was swarming

with American and Canadian soldiers.

- [John] The students overheard troops using strange words

like Utah, Overlord, Omaha.

They didn't think they were secrets,

just cool sounding words for their headmaster's puzzles.

- [Don] And to think, had the D-Day invasion failed,

Leonard Dawe would've faced a firing squad for treason.

And he most likely would've been convicted on

nothing more than an incredible string of coincidences.

- [Danny] In 1831, a walk along Scotland's coastal sand dunes

uncovers the first pieces of a tantalizing puzzle.

- Malcolm MacLeod, or Sprot, as he's known to his friends,

is out tending his cattle amongst the sand dunes

on the Isle of Lewis in Scotland

when he comes upon something strange in the sand.

It looks like a chess piece.

- Sprot starts digging.

And before he knows it,

he's pulling out all these ornate game pieces.

78 chess pieces to be exact, and 14 backgammon pieces.

- He doesn't know what to do with them,

so he sells them for around 30 pounds.

They change hands a few more times,

and eventually,

they end up at the Society of Antiquaries of Scotland

in Edinburgh.

- [Danny] When experts take a look,

they can't believe what they see.

- [Dr. Hakeem] Turns out, these chess pieces aren't just old,

they're medieval

- Researchers date them to about 1150 to 1200 AD.

And then, they realize that these pieces

are made out of walrus ivory.

- [Andrew] Walrus ivory was so rare and valuable in the Middle

Ages that it was referred to as "Arctic gold."

- [Dr. Hakeem] The craftsmanship on the pieces is stunning.

The faces are so expressive, they're almost human.

These are some of the most well-preserved

medieval chess pieces ever discovered.

And they're also among

some of the very first medieval objects

in the British Museum.

- [Danny] Today, they're known as the Lewis Chessman.

But the discovery also sparks a new mystery.

The set is incomplete.

- [Adam] It appears to be a mix of multiple sets.

But several pieces, four rooks, a night, and multiple pawns

are missing.

- [Danny] And they remain missing for nearly 200 years,

until an unexpected encounter in 2019.

- [Adam] In Edinburgh, Scotland, a woman walks into Sotheby's

with a little figurine, and she wants to have it appraised.

- [Andrew] She doesn't know what it is,

but says her grandfather, who was an antiques dealer,

acquired it from 1964.

It's a warrior with a helmet, a shield, and a sword.

- [Dr. Hakeem] She tells the appraisers he bought it

for five pounds.

But he didn't think much of it, so he threw it in a

drawer, and there it remained for 55 years.

- [Adam] At Sotheby's, expert Alexander Kader examines the

piece, and his heart nearly stops.

The level of craftsmanship is unmistakable,

and every test confirms it.

It's one of the missing Lewis Chessman warders,

which functions like a rook in modern chess.

- [Dr. Hakeem] Since the Scottish woman is the owner,

she decides to cash in and sell it

rather than donating it to the museum.

So now, this is the first Lewis Chessman

to be available for private collections.

- [Danny] Around the same time,

interest in this age-old artifact is soaring,

thanks to a boost by a blockbuster cameo.

- [Andrew] In 2001, the Lewis Chessman became part of a movie,

inspiring the look of the giant enchanted chessboard

in the film "Harry Potter and the Sorcerer's Stone."

So when it hits the market, the art world goes crazy.

- [Danny] Bidding starts low but climbs quickly.

The final price:

$929,000.

- [Andrew] This is one of the most profitable antique sales

in history.

An item originally purchased for five pounds

sells for nearly $1 million.

- [Danny] 9,000 miles away,

another stretch of dunes guards a different kind of secret.

- [Don] In January 2018, Tonya Illman is strolling along

the shoreline of Wedge Island in Western Australia.

As she passes some sand dunes, something catches her eye.

- She makes her way to this object

and picks it up off the ground,

and she notices that it's a very distinct-looking bottle

with some raised lettering on it.

Then she hears a faint rattle on the inside of this bottle.

And as she looks inside,

she sees this small, rolled-up piece of paper.

- [Danny] It's like something out of an adventure tale,

an actual real life message in a bottle.

- [Kavitha] Tonya brings it home to show her husband, Kym.

But as they try to extract the paper,

they realize it's super fragile, water-logged, and decaying.

- [Don] They worry that any wrong move

might destroy the whole thing,

so they carefully place it in a very low-heated oven

to dry it out.

Slowly, some faded writing appears.

- [Alex] It's written in German.

And at the bottom of the page

are a bunch of random numbers and blank spaces.

But from the look of it,

it doesn't appear to be a personal note,

it looks like an official document.

- [Don] Kym can tell it contains some printed text

requesting coordinates

with some handwritten entries in the blank spaces,

and scrawled faintly in the center of the form

is the name Paula.

- [Danny] To get to the bottom of the strange clues,

Kym and Tonya turned to the Western Australian Museum.

- [Sami] Experts find out that the name Paula

doesn't refer to a person,

it actually refers to a ship.

And they soon discover that the ship Paula

was part of this massive oceanographic experiment.

- [Danny] Even more incredible,

it took place over 150 years ago.

- [Kavitha] Between 1864 and 1933,

thousands of bottles with messages in them

were launched overboard from ships,

part of a 70-year study to examine ocean currents.

- [Don] Each message contained the ship's name, coordinates,

data, and instructions for whoever found it.

"Record where and when the bottle ended up,

then mail it back to the German Naval Observatory."

- [Alex] When combined with data from all the other bottles,

scientists could map the ocean current movement

from all over the globe.

- It might sound primitive now,

but at the time, it was pretty groundbreaking.

It was one of the first comprehensive

oceanography studies ever.

- [Don] Of the thousands of bottles released

during this German oceanographic experiment,

only 662 messages had ever been returned

before Tonya and Kym's discovery.

- [Sami] This particular message in bottle

that was launched by the crew of the Paula

took place on June 12th, 1886,

roughly 590 miles off the coast of Australia.

That makes this 132-year-old discovery

the oldest message in a bottle ever found.

- [Danny] When you picture war heroes,

you probably think of great generals on the front lines.

But during World War I,

a very different kind of hero emerges.

- It's 1915 in England, and World War I is raging.

[artillery fires]

But in the back rooms of Britain's war office,

a different battle is underway.

- [John] Here, a mostly female team of workers

sift through thousands of letters every day.

Under special wartime powers,

they monitor all correspondents

entering or leaving the country.

They're checking for any details or information

that might accidentally provide Britain's enemies

with an advantage in the war.

- [Andrew] One gray morning,

an assistant censor clerk named Mabel Elliot

is sorting through her pile.

The letter she opens

appears to be routine business correspondence,

very dry, talk of trade and deals,

but something about it feels off.

- [John] Mabel holds the paper up to the light

and notices a slight discoloration between the lines.

- [Danny] She's seen enough letters

to know these marks aren't accidental.

So Mabel makes moves to confirm her suspicion.

- [Martin] She gently exposes the letter to low heat

from a clothes iron,

and as the heat reaches the paper,

suddenly those stains and splotches,

they take the form of clear and distinct lettering.

What she was seeing on the letter

was the telltale signs of invisible ink.

- [Adam] The secret message dictates the deployment of ships

all along Britain's highly vulnerable coastline.

[artillery fires]

It details the deployment of troops, the numbers,

the types of equipment that are defending London.

And that information in the hands of the Germans

could have easily turned the tide of the war

and destroyed Britain.

- [Andrew] British intelligence is able to trace the letter

to a German-born American named Anton Kuepferle.

They find him living under an assumed identity

in a London flat

and promptly arrest him.

- [Danny] After hours of questioning,

Kuepferle finally confesses.

- [Adam] He admits that

he's not a German-born American wool merchant,

he is in fact a German military captain

who is sent to Britain as a spy.

- [John] As British agents continue to drill him,

the terrified spy reveals the names

of two other German agents operating on British soil.

From there,

the confession helps crack open an entire hidden spy network

operating in the country.

- [Martin] Kuepferle is put on trial at the Tower of London

under conditions of complete secrecy,

and Mabel is the star witness in that trial.

However, with the knowledge that German intelligence

would do anything to try to silence her,

her testimony is done under an alias

to protect her identity.

- [Danny] Before Kuepferle is sentenced,

he's discovered hanging in his cell.

- [Andrew] After the war, Mabel goes on to become a business

manager at the Royal Society of Chemistry.

For decades, no one knows about Mabel's role

in uncovering one of World War I's most dangerous spy rings.

- [Adam] It isn't until almost 100 years later in 2011

when archivists finally stumble upon her name,

and Mabel Elliot emerges as a hidden hero of World War I.

- [Danny] Some messages hide in enemy letters.

Others are sealed in objects so sacred

no one would ever think to look.

- [Don] It's 2017 in northern Spain,

and restoration artists are hunched over their benches

in a quiet church workshop.

Their latest project

is restoring an 18th-century wooden statue

of Jesus on the cross.

- [Hugo] This isn't just any crucifix.

This is the church's centerpiece.

Known as the Cristo del Miserere,

this near life-sized statue has hung over worshipers

for over 200 years.

- The restorationists take this wooden statue

and they're examining it all over,

looking for any kind of wear or damage on it.

- [Don] At first, their examination reveals

pretty normal wear and tear for the old relic,

splintered wood, cracks in the varnish.

But when they turn the statue over,

they see something strange.

- [Danny] Along the seam of the wooden loincloth

draped around Jesus's waist,

there's an unusual gap.

- [Nicola] Carefully, carefully they lift up

the back of this piece of wood

and notice that inside there's a hidden compartment.

And amazingly, inside the compartment,

they find two delicate scrolls

that have been rolled up and placed inside that cavity.

- [Danny] As they gently unroll the scrolls,

it becomes clear they're holding letters

written over two centuries ago.

- [Hugo] It's dated to the year 1777,

and they're written in an elegant script on sheepskin.

The author is Joaquin Minguez,

who was the chaplain of the Cathedral of Burgo de Osma.

The scrolls vividly describe life in the 18th century.

- [Danny] But between the lines,

Minguez's words reveal something darker.

- [Nicola] He uses the scrolls to comment candidly

on two particularly powerful things going on

at this moment in time.

One is the reign of King Carlos III of Spain,

the other is the Spanish Inquisition.

- The Spanish Inquisition was established

as a religious court in 1478,

but it also was a brutal enforcer of orthodoxy

using torture and execution to quash any dissent.

- [Hugo] The court helped consolidate power

in the newly unified Spanish monarchy.

It targeted Jews, Muslims, Protestants,

even Catholics who showed any signs of wavering

from church orthodoxy.

- [Don] For a Catholic chaplain like Minguez,

criticizing either the Inquisition

or the King's policies was treason.

And if anyone were to find out,

he would face imprisonment, torture, or execution.

[man cries] [swords clash]

- [Danny] So he hid his words in the one place

no one in this devoutly Catholic country would ever look.

- [Hugo] Historians believe the letters were meant to be

some sort of time capsule for future generations.

And so, after careful documentation,

the letters were sent to the Archbishop of Burgos

to be carefully preserved and archived.

But in a poetic gesture,

copies of the two original letters

were placed back into the hidden compartment

of the crucifix.

- [Don] Today, the statue hangs once again,

where it continues to gaze down upon the devout.

- [Danny] Most metal detector finds are pretty ordinary,

but this one is something that stops even the experts

in their tracks.

- [Andrew] It's a cold, crisp day in December 2022

in northern Belgium.

Amateur treasure hunter named Patrick Schuermans

is out sweeping his metal detector back and forth

across a farmer's field.

[metal detector beeps]

- [Sami] In the past, Patrick had found a few old coins,

but nothing really worth bragging about.

But for Patrick, it's more about the thrill of discovery,

what could be underneath the ground.

And on this particular day,

as Patrick is sweeping his metal detector,

[metal detector beeps]

it goes off, it starts to beep,

and so he puts it down, gets down on his hands and knees

and starts digging.

- [Danny] What he pulls from the earth is no old coin,

but an object unlike anything he's ever seen.

- It's small, it looks bronze,

it's decorated with geometric lines,

and it has a small sphere right at the top.

- [Sami] His heart is racing,

and he knows that something about this has to be important.

So he takes it to the experts at the Gallo-Roman Museum

in the nearby town of Tongeren.

- [Danny] When archeologists examine the artifact,

they immediately recognize it.

It's one of history's most enduring puzzles.

- [Andrew] It's known as a Roman dodecahedron.

It's a 12-sided box, hollow, with a hole in each phase.

You can think of it like a combination of a wiffle ball

and a 12-sided die.

- [Hugo] Over a hundred of these dodecahedrons have been found.

When they pop up,

it's usually in northern Europe

in places that used to be part of the ancient Roman Empire.

- [Sami] Each dodecahedron is unique.

Some of them are about the size of a marble,

whereas others can be about the size of your fist.

Based on the design, researchers are able to conclude

that this particular

dodecahedron that Patrick brings them

is around 1600 years old.

- [Danny] While experts can date it,

even after years of study,

no one knows what these things were for.

- [Andrew] Some think that this is an ancient dice

used in a high-stakes Roman gambling game.

Others speculate that,

because so many have been found near military sites,

that this was some kind of military tool

[swords clashing]

may be used to calculate distances to targets.

- [Sami] Some even suggest a more mythical

and a more mystical meaning behind them.

As Christianity was on the rise in the Roman Empire,

it suggested that Roman pagans went underground,

and these objects were a part of their secret rituals.

- [Danny] Whatever their significance,

the meticulous design

suggests that they held real importance.

- [Hugo] Every dodecahedron is unique,

and they were obviously crafted with great skill and care.

And yet, no Roman document mentions them.

- [Sami] As for the piece that Patrick discovers,

he donates it to the Gallo-Roman Museum,

where it's on display next to another dodecahedron

that was discovered back in 1939.

- [Danny] Some puzzles are forged in bronze,

others are hidden between the pages of an old book,

waiting for the right set of eyes to find them.

- [Hugo] It's 2019 at the University of Cambridge's

Special Collections.

This is the place where the university keeps

old books and manuscripts dating back thousands of years.

- [Andrew] Archivist Sean Collins is flipping through

a 16th-century property registry,

essentially a record of who owned what land centuries ago.

In an archive full of exciting and arcane ancient texts,

this is one of the collection's more mundane items.

- [Sami] But as she looks through the book,

something feels a little bit off.

The binding feels a little too thick

and also a little too stiff.

- [Danny] Most people would just move on,

but Collins has a keen eye for detail.

- [Nicola] She holds the book up to the light,

and that's when she notices

a piece of what seems to be parchment

stitched right inside the 16th-century binding.

- [Sami] Sean looks a bit closer at this parchment,

and she makes out ancient writing

that appears to be old French,

but she can't read it.

- [Danny] Luckily, she has a colleague who can.

- [Andrew] When she squints at the page, two names jump out,

Arthur and Merlin.

- [Hugo] Arthur and Merlin, of course, are King Arthur

and Merlin the wizard from Camelot.

They're the guys from all of those stories and books,

movies, the Broadway musical.

- [Danny] If this unassuming book

holds a long lost King Arthur tale,

unlocking it will take a different kind of magic.

- [Nicola] Now, in order to read what this full parchment says,

they need to remove it from the binding,

but that would completely destroy it.

And so, they turn to technology.

- [Sami] They use something that's called multi-spectral

imaging.

Basically what this is,

is technology that takes thousands of photos of an item

using all manner of light,

everything from UV to infrared.

- [Andrew] Each wavelength reveals a different feature

of the hidden text,

and it enables them to scan the entire manuscript

without touching it.

- [Danny] After taking thousands of images,

computer programs are able to reconstruct the text.

- [Sami] What emerges is a brand new 800-year-old

3000-word Arthurian story.

- [Hugo] It comes from the Vulgate Cycle,

which is sort of like the medieval equivalent

of a cinematic universe.

It was written between 1210 and 1230,

and it's the collection of stories

that catapulted Arthur and his knights

to fame all across Europe.

- [Sami] Now, most stories of this period

focus on the characters of Lancelot, Guinevere, and Arthur,

a lot of like soap opera-style drama

that was considered to be real spicy for the 13th century.

- [Danny] But this story is different.

[swords clashing]

- [Hugo] It depicts Arthur as a military leader.

He's defending England against Saxon invaders.

And it shows Merlin using some serious magical powers

as a wizard.

He's conjuring mist to hide Arthur's troops.

He's also summoning storms to try to thwart enemy archers.

- [Andrew] This new story

fills in a crucial piece of the bigger picture.

It portrays a much more warrior, like Arthur,

and a much more magically powerful Merlin

than we see in some later stories.

- [Nicola] It makes you wonder,

"If this story slipped through the cracks,

what other legends might be lost,

just hidden inside the bindings of an ancient book?"

- [Danny] When divers uncover a baffling formation

on the ocean floor,

the quest to learn more about it begins.

- [Dr. Hakeem] It's 1995,

and a group of divers are exploring the Philippine Sea

off the coast of this remote Japanese island.

They're about 80 feet down,

following the school of parrotfish,

when suddenly their eyes catch something unusual.

- [Andrew] It looks like a perfect geometric formation

etched into the sea floor.

It's about six feet across

and is comprised of variety of ridges, peaks, valleys,

seemingly meticulously carved right into the sand.

- It looks like a massive mandala or elaborate snowflake.

Concentric circles, rays radiating out from the center,

framed by pebbles and shell fragments.

- The divers swim closer for a better look,

and what they found looks too perfect to be natural,

but also too strange to be manmade.

- [Danny] They snapped some photos

and raced to shore to share their strange discovery.

- Back on land,

they show some pictures to local fishermen.

And the more these photos are circulated,

the more of a stir they cause.

- [Dr. Hakeem] Eventually, the photos air on a local

TV program.

And after that, they go global.

And the more people that see them,

the more ideas come about,

and some of them are truly out of this world.

- [Andrew] Some self-proclaimed experts

say that these are too mathematically precise

to be naturally occurring.

And among those, some see this as proof

of an alien civilization

trying to our attention.

- [Micah] UFO enthusiasts began to compare these shapes

to the famous crop circles

that started appearing in fields during the 1980s and 1990s.

And although those were eventually ruled out

to be elaborate hoaxes,

these formations appeared underwater,

and no one could explain

exactly how they could have gotten there.

- [Danny] Who created these shapes and why

remains a mystery for another 16 years.

- [Andrew] In 2011,

a Japanese marine biologist

and underwater photographer named Yoji Ookata

decides he's going to get to the bottom of this

once and for all.

He spent nearly 50 years documenting sea life,

and with the help of a team,

installs time-lapse cameras underwater

just off the coast

and waits.

- [Danny] The footage they capture blows everyone away.

- [Dr. Hakeem] Turns out the architect

of these magnificent formations aren't aliens at all.

It's a tiny, previously undocumented

species of pufferfish.

- [Andrew] The footage shows a male working day and night.

He uses his tiny fins like rakes

sculpting the valleys and ridges,

slowly moving pebbles and seashell fragments one at a time

into place around the perimeter as decoration.

- [Micah] Ookata is astounded.

This little pufferfish is working like a builder

on the sea floor laying tiles for a masterpiece.

And the geometric designs he creates

would even impress human architects.

- [Danny] It's not just for show.

These designs serve a practical purpose.

- [Dr. Hakeem] The geometric formations actually function

as a sophisticated current control mechanism.

By making these ridges and valleys,

that disrupts the water flow across the seabed.

And as a result, in the center of the pattern,

there is an area of calm water,

and that area is perfect for the female to lay her eggs.

- [Austin] If the female pufferfish is impressed

with the male's architectural skills,

she'll mate with him.

- [Andrew] Even with all of the underwater footage,

scientists are still unsure

what criteria female pufferfish use

to judge a potential mate's design.

Is it beauty?

Symmetry? The placement of shells?

Size?

We still don't know.

- [Danny] In the middle of Cold War surveillance,

a mysterious sound deep in the ocean unlocks a discovery

that has nothing to do with enemy subs.

[water splashing]

- [Don] It's the 1950s, and the Cold War is in full swing.

As the US and USSR build up their nuclear arsenals,

deep beneath the surface of the Atlantic Ocean,

a different technological arms race is unfolding

in complete secrecy.

- [Dr. Hakeem] Frank Watlington is a US Navy engineer

stationed at a classified underwater listening post

off the coast of Bermuda.

This site is part of a network known as SOSUS,

the sound surveillance System.

- [Don] SOSUS is one of the most ambitious engineering projects

of the Cold War.

It's a massive array of underwater microphones,

called hydrophones,

all positioned across the ocean floor.

Each microphone is wired to a coastal processing center.

- [Jen] Watlington's mission is to search the sea

for the acoustic signatures

that might indicate the presence of Soviet submarines

prowling America's coastal waters.

- [Austin] One day, he hears something,

but it doesn't sound like the mechanical signature

of a submarine.

Instead, it's long, low groans

followed by high piercing cries.

[humpback whale groans]

- [Danny] Watlington considers a disturbing possibility

that this is the sound of a new weapon.

[missile engine roars]

- [Jen] He comes through shipping records and title

charts looking for any evidence of what these sounds might be,

but he can't figure it out.

- [Don] Eventually, he decides to place hydrophones

closer to the surface

to see if he can track whatever it is

in the vicinity of where he is hearing the sounds.

Sure enough, one day,

as he's listening to the long, low notes he notices,

[humpback whale groans]

a humpback whale swim right past his microphone.

- [Danny] It's a breakthrough.

These aren't random noises.

The humpbacks are communicating,

[humpback whale groans]

but Watlington can't tell a soul.

[water splashes]

[audio recorder beeps]

- [Dr. Hakeem] SOSUS is top secret.

Sharing what he thinks he's figured out

with marine biologists

would risk exposing this classified government program.

So Watlington has no choice.

He has to keep his data and his theory secret

for the next 15 years.

- [Danny] In 1967,

when the recordings are finally declassified,

Watlington is able to share his amazing discovery.

- [Jen] He reaches out to Dr. Roger Payne,

a biologist studying animal vocalizations.

He travels to Bermuda to listen to these recordings.

And when he hears them, he is stunned.

[audio player buzzing]

[humpback whale groans]

- [Dr. Hakeem] These sounds aren't random.

They're fixed, repeated patterns of rhythmic sounds.

In other words, they're songs.

These compositions can last

from anywhere from six to 30 minutes,

and the whales will repeat them for hours on end.

- [Don] Eventually, he discovers that all humpback whales

in a region

sing nearly identical versions of the same song,

and the song gradually evolves over time.

[water splashes]

- [Danny] Eager to share their discovery,

Watlington and Payne released an album in 1970,

"Songs of the Humpback Whale."

- [Dr. Hakeem] The album turns out to be a surprise sensation.

They quickly sell about 125,000 copies

and eventually go multi-platinum.

It becomes the highest selling environmental album

of all time.

- [Don] Frank Watlington's ears were trained

to detect Cold War danger beneath the waves.

But instead, he discovered music that moved not just whales,

but people as well.

[humpback whale groans]

- [Danny] From coded clues to covert coins,

tonight showed us that even the most unassuming objects

can hold world-changing secrets.

I'm Danny Trejo.

Thanks for watching "Mysteries Unearthed."