A strange group of rusting structures off the coast of England, a dilapidated mediaeval-style castle in the heart of urban America and one of the biggest machines ever built lying forgotten in a German field. Once these extraordinary places and objects were at the cutting edge of design and construction, but now they stand disused, sometimes contaminated and sometimes dangerous. But who was it that built these mysterious structures? What incredible stories surround them? What secrets do they hold? And why were they abandoned?

Seven huge steel boxes rise 80-feet out of the water off the coast of England at the mouth of the River Thames. Now rusting and derelict, The Red Sands Sea Fort was originally built as a first line of defence to deter the Nazi threat to London. Successfully helping the Allies to victory in 1945, the project is one of the most extraordinary engineering successes of World War II.

Also in this episode, a sinister-looking deserted Cold War concrete pyramid in North Dakota; a vast empty complex located in the heart of a Philadelphia; and a 4,000-tonne corroding mass of steel, left to rot in a field in Eastern Germany.

Learn about the strange-looking, derelict military facilities in Farnborough, which were once wind tunnels that played a vital role in WWII.

The Canfranc Railway Station is an elaborate abandoned Nazi railway station built near a town of only 500 people in the Pyrenees in Spain. But why was it built there and what secrets does it hold?

Also examined in this episode is the Salton Sea Navy Base in California - a military post in the middle of the desert in the American west, the Kola Superdeep borehole - a wrecked record-holding Arctic facility in Russia that goes deep, deep underground, and a huge tower looming over an industrial area in Belgium. All of these extraordinary places and objects were at the cutting edge of design and construction, but now they stand disused, sometimes contaminated and sometimes dangerous.

This week, find out why Fordlandia Rubber Town, a symbol of the American dream first established by Henry Ford in the 1920s, is now left rotting in the Amazonian rainforest. Also, what secrets do the enormous monoliths scattered across a secret forest complex in Eastern Poland hold? And what secrets does a fortified corridor of death with a Cold war past stretching for miles across Hötensleben, Germany hold? And a bizarre structure in South Western France built to speed trade was once at the forefront of design, now lies disused and abandoned, but why?

A lost highway in the Brazilian jungle, a forgotten bunker system in the French Alps and a man-made island in the shadow of the Statue of Liberty. Who built them, and why?

The programme looks at a mysterious group of rusting ships stranded in an arid desert, a monstrous defensive line on the snow-covered peaks of the Italian Alps, a ghostly collection of buildings, and the sunken remains of a unique vessel.

An abandoned prison beneath the water, a tunnel in the heart of a mountain, concrete towers hidden in the woods and a rusting coastal relic.

Concrete channels hidden in a mountaintop forest, a collapsing bridge, a marooned military base and the upright rusting carcass of ship.

A devastated cliff-top ruin, an extraordinarily tall tower, a concrete structure stranded at sea and a heavy metal monster in a field all feature.

Hidden tunnels that saw a city prosper, a sunken wreck with a remarkable past, a concrete wartime dome and a mysterious Cold War building.

A village ruin, pitted and scarred, a ghostly fleet of ships, a bridge to nowhere hidden in a forest and strange metal structures in a wood.

An eerie, empty country village which hides a sad secret, a mysterious tower battered by the elements and a disused railway deep beneath the streets of a city.

A settlement in Argentina destroyed by floods, a town in the US that has been erased, and a Soviet dream-town that turned into a nuclear nightmare.

A seemingly endless concrete line stretching through the French countryside, which sits as a monument to a discarded engineering advancement.

A little-known dark past explains the vast monolithic structures that dominate the small British island of Guernsey.

Projects include a maze of tunnels filled with haunting remains beneath the streets of Paris and a strange formation of domed structures hovering over the waters off Florida.

A town in West Virginia that fell victim to the pace of change when steam trains became obsolete and an underground complex in Italy that had been abandoned for nearly 2,000 years.

Features a ruined compound in Colombia which was once home to Pablo Escobar and alien-looking structures with no apparent purpose, isolated in an empty English marshland in Denge, near Dungeness in Kent. But how and why were they ever built at all, and why are they now left abandoned?

A formerly luxurious and strategic mountain-top villa on the island of Rhodes in the Mediterranean that's been ravaged by acts of revenge by locals since 1955.

A strange-looking deserted town with an almost supernatural atmosphere on a remote Norwegian archipelago in the Arctic Ocean was in fact an ambitious Soviet mining outpost with a tragic history. Also, a collection of imposing buildings on the southern tip of Australia, the remains of curious-looking basins emerging from the waves in the shadow of the Golden Gate Bridge and the ruins of a monumental construction project in southern Germany that was a ruthless regime's deadly prototype.

Still standing today, a fierce-looking prison and an innocuous looking office building in Berlin were actually the headquarters of a feared and ruthless organisation - the Stasi. Also, a covert Communist base hid Cold War submarines for Tito, the former leader of Yugoslavia on the island of Vis. A seemingly innocuous sports centre hides a sinister underground bunker. And the former HQ of the Soviet Army in East Germany was a forbidden Soviet city within a city.

A vast snowcovered monster in the icy wilderness of southern Alaska, a ruined super structure that overshadows everything around it in and a landscape of confusing and surprising structures that once represented a bold statement of Spain's plans for the future. Plus, a long, winding formation that was once supposed to help defend Hitler's Third Reich. And in Budapest, Hungary, the stripped skeleton of an industrial relic lies rusting away.

A pioneering complex marked by both glory and tragedy that's soon to be lost forever, and towering remains from an industrial age.

The desert town that faced a disaster of biblical proportions. Plus, vast coastal ruins that reveal a past once wiped from history.

The underground base with the power to destroy a nation, the site linked with an attempt to kill a dictator, and an ancient world discovered in the American wilderness.

Claustrophobic prison cells that contain a story worthy of international acclaim, and a vast mountainside complex that held the power to change the world.

A secretive underground base that concealed the power to destroy nations, and a sprawling industrial relic clinging to the edge of an unforgiving waterfall.

Including an exploration of forgotten relics from the defence of America's homeland, at Fort Jackson, USA, concealed by the banks of the Mississippi River; a concrete behemoth at Lorient Sub Base, on the coast of France, that proved invulnerable to enemy bombardment; and a ghostly ruin at Gwrych that is now home to a haunting presence.

An American prison for the violent and deranged with links to an infamous cult leader, and a cavernous tunnel network in France offering shelter from unrelenting bombardment.

An Albanian village home to Allied secret agents, devastated for resisting the Nazi war machine, and a notorious asylum in America that enforced lobotomies on a terrifying scale.

What happened to an infamous pirate city in Jamaica? Also, a grim gulag in Croatia and a Louisiana plantation caught up in the aftermath of the American Civil War.

Examining a ghost island once belonging to a secretive country on the fringes of Europe. Also, a haunting site in the UK with evidence of strange burial practices.

Within a dense Polish woodland sits a forgotten complex with an explosive history. Also, grand coastal defences in Ghana reveal a tortured past.

A complex of stone buildings near Hadrian's Wall that were built to keep Northern hoards at bay. Also, a top secret military facility in the American Midwest.

An extended special featuring a deserted Caribbean city, an American ghost town still burning and an Arctic settlement facing a terrifying future.

A now silent site that played a pivotal role defending the U.S through the 20th century. Plus, a crumbling Italian fortress and a ghostly Ukrainian mansion.

A juggernaut of Soviet engineering which was crucial to the international space race. Deserted Scottish coastal defences and a complex that's crucial to American history.

The mysterious Cachtice Castle home to Elizabeth Bathory, said to have killed over 600 girls and a mysterious structure on the 38th parallel.

A small isolated country littered with strange concrete mushrooms and a secret Japanese facility that was once at the forefront of weapons technology.

An impressive compound commandeered and repurposed by a brutal regime and an eerie complex off the coast of Ireland that became the biggest of its kind.

Legendary film sets with surprising pasts and real locations that inspired Hollywood. Within these decaying structures are the echoes of history.

In North Wales a secret facility which once manufactured mustard gas and enriched uranium lies in ruins. In Malta is a luxurious quarantine facility, that hides a dark secret.

Ruins of a vast industrial ghost town in the United States, a windswept Scottish island and the remains of a resort in Japan that watched a city burn.

An engineering masterpiece carved into the cliff-face, and a long-range beacon that transmitted one of the most infamous messages in American history.

An American desert canyon where fortunes were made and lives were lost, and an island fortress in Scotland with an Achilles heel.

An iron monster lost in the Alaskan tundra, a Crusader fort thrown into a modern conflict, and a prison built to house a mafia kingpin.

A real-life concrete jungle in America's 'Rust Belt', and an industrial facility that brought energy to a remote corner of the world.

A Middle Eastern region littered with ruins and a strange facility in Taiwan that struck fear into the hearts of those who knew its true purpose.

Eerie ruins hiding in the forested hills of Arkansas, USA, and a disintegrating gulag in Albania that housed enemies of the state.

A volcanic island just off Taiwan containing chilling ruins from its darkest era, and a miniature railway that lies forgotten in the woods of Arkansas.

A fairy-tale castle that staged one of the strangest stories of the Second World War and a haunting complex on an old American Frontier.

Bizarrely-shaped huts in India, once home to global superstars, are now eerily quiet and neglected, and a shattered compound in Colombia linked to a criminal mastermind.

The home of an African dictator and a sporting hero, and the facility that held apartheid's greatest critic are abandoned, but still have unique stories to tell.

Exploring a ghost town in Colorado, the remnants of an industrial enterprise in Puerto Rico, and a remote village on Cyprus.

Exploring a jungle refuge concealing a story of royal deceit, nuclear bunkers infiltrated by outsiders, and a haunted hospital marked by scandal.

Exploring a beachside resort with ties to the Russian mafia, a windswept base hiding lifesaving technology, and a site in Iowa plagued by its past.

Exploring a bizarre block in Taiwan resembling a giant speaker, a pioneering venture in Alaska, and an alpine village that masks a military beast.

An ominous tower in the forests of Croatia, a New York City complex that broke the mould, and a grand facility guarding the London riverbanks.

Exploring a desert island with an infected past adrift from the US mainland, the brutalist palace of a mad Bulgarian dictator, and a doomed top-secret Nazi project.

Featuring Italian ruins immortalised by Hollywood, a crumbling Chilean city with two lives and a brutalist Scottish relic whose prayers went unanswered.

Exploring a luxury resort that conceals a top-secret facility, a mysterious complex in Bali struck by disaster, and a relic of hope near Jerusalem.

Exploring a dystopian powerhouse in Pennsylvania, USA, a fairy-tale castle in Poland and AngloSaxon religious ruins across vast plains of Scotland.

Exploring a bloody battleground on the Pacific Island of Peleliu and an ominous military stronghold in Russia.

This episode travels to Chile, the Maltese capital Valleta, Havana and Germany, to reveal: honeymoon home of a young princess that offered her a glimpse of freedom; grand monuments designed by the most notorious dictator of the twentieth century; a sprawling industrial complex?the site of a ruthless disappearance; and?the artistic dream of?a revolutionary now in?ruins.

Exploring a once lavish palace in Iraq, the Sathorn Unique, an epic ghost tower in Thailand, and a former sports stadium in Georgia, USA

Exploring the remains of a pioneering industry town in Ohio, a once beautiful Croatian resort bombarded by enemy fire, and an otherworldly garden of Eden in Mexico.

The graffitied remains of a correctional facility in Atlanta, USA with a controversial and unexpected past, forgotten remnants of fraud and fusion on the Western border of Argentina and a mysterious ancient complex built by a devoted Khmer King in the jungles of Cambodia.

Exploring a military strong-hold in the Philippines, a facility that spawned an American sporting great, and an English relic that hosted a cinematic sensation.

Exploring a ruined castle above a German village, a rural town in Idaho, a futuristic skyscraper in Johannesburg and a fantasy world outside of Buenos Aires.

Exploring a British fort that became a bizzare zoo, a brutalist school for Communist top brass and a lost world hides secrets of a vanished people.

Exploring a crumbling dam hidden in the Welsh valleys, a quaint outpost on a paradise island, and a mastery of ancient engineering that brought life to the planes of Mexico.

Exploring a complex in Georgia pointing into deep space that almost discovered a signal from aliens.

Exploring Hartwood, a haunting facility in Scotland, ruins of an ancient city in Iraq and a scandal hit town in New Mexico.

Exploring a royal retreat caught in a web of corruption, an engineering marvel hidden behind the Niagara Falls in Canada, and a subterranean treasure.

Explore Oradour-sur-Glane, a French town drenched in infamy, the victim of a notorious raid, Alcatraz, a facility famed for breakouts, subjected to a daring break-in, and Sealand, a micronation off the English coast, stormed by a band of mercenaries.

Exploring a series of vaults, hidden from view in Edinburgh, Scotland that tell a murky story of opportunity, crime and destitution.

Exploring the remains of an ingenious sky-high solution to a ground-based problem, Chiatura, once know as the Venice of the air

Exploring Agdam, a city in Azerbaijan raised to the ground in a conflict decided by a new weapon of war.

Exploring an industrial ruin in the Florida Everglades that once competed in the greatest race humankind has ever witnessed.

Exploring traces of a mass deception hidden at Ponte Dirillo in Italy, as well as a once lavish theatre in Ohio and an ancient city with a poisonous secret.

Explores a dense forest near the Czech capital of Prague that hides Houska Castle, an eerie keep that has been subject to long-standing rumours that it possesses supernatural powers.

Exploring a grand structure in Hull that was reduced to rubble by Hitler's planes, Casa Albero in Italy, USS Hornet in California and the Sofia tunnels.

Exploring a decrepit Liberian landmark with American origins, a desolate town in Belgium and a pioneering scientific structure in Cleveland.

Exploring the Dew Drop Inn in New Orleans that dared to take on the authorities and paid the price and Belgica Fort, built to defend an unlikely treasure.

Exploring Air Studios, on the Island of Montserrat, that became a mecca for rock legends. Also Tskaltubo, in Georgia, built to host a fearsome dictator.

Exploring Haludovo Palace Hotel in Croatia, Wolf's Lair, a German military complex and Herouni Mirror Radio Telescope - a pioneering facility in Armenia.

Exploring a theme park in Buenos Aires built in a time of terror and dogged by controversy, and a jaw-dropping collection of castles in Turkey.

Exploring Dover Commando Fortress in South East England, where traces of a top-secret Commando raid are still visible.

A symbol of national pride that became a symbol of excess in the Turkish capital of Ankara.

Exploring Yongma Land - a South Korean dreamland given a second life from the most unlikely of places.

Exploring Old Joliet Prison, a battered facility near Chicago that descended into open war, but then hosted the Blues Brothers!

Exploring Chateau Aubery on the island of Martinique, where a criminal kingpin wiped out the opposition.

Exploring Castel Volturno in Campana in Italy, Colorado and HMP Shepton Mallet in Somerset.

Exploring the Apollo Movie Theatre in Tbilisi, Georgia, an ornate shrine to Soviet propaganda.

Exploring a country estate in Ireland where family divisions reflected a national struggle and was caught in the crossfire.

Exploring Anchieta, a tropical island complex in Brazil and the scene of a dramatic uprising.

Exploring the ruined site of Troy, that helped decode one of the world's most enduring mysteries.

Exploring Seodaemun Prison, a facility in Seoul that helped spawn a legend known as South Korea's Joan of Arc.

Exploring Opa-Locka City Hall, a strange structure that began as the dream of an American Renaissance man, but soon turned into a nightmare.

We explore Namibia's arid Skeleton Coast, where traces of a brutal but once vital industry lie scattered.

We head to the Tunisian desert to explore a vast chain of ruins that once stood in the way of Allied Victory - until a band of rogue heroes uncovered their weakness.

We explore Fort Amador, the site of an American invasion in Panama, and a grisly Polish facility that once caged members of a revolutionary movement.

We explore Schindler's Ark in the Czech Republic, a secret refuge in Europe's killing fields, and a lost Amazonian paradise deep in the Brazilian rainforest.

We visit the decaying remains of Old Essex County Jail in New Jersey, a facility that became a powder keg of injustice that was set to explode.

We visit the Polish city of Walbrzych, where a fairytale castle on a cliff conceals a vast subterranean tunnel network linked to a legend of lost Nazi gold.

We explore Fort Sherman, a jungle stronghold in Panama built to defend a prized American possession that soon faced the threat of an elaborate Nazi conspiracy.

Exploring an Oklahoman town so wealthy it inspired a Hollywood film.