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.

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.

A sprawling Wild West ghost town sits peaceful and abandoned in Montana, USA, but is still haunted by tales of murder, corruption and buried treasure. Also, a cold, dark, underground mountain network that cost the lives of thousands... the crumbling ruins of an English industry that turned poison into profit... a peaceful village that was shattered by the terrors of war.

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.

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.

A creepy collection of buildings, monuments hidden in a Parisian park and an eerie graveyard of discarded ships strewn along the banks of a mighty river.

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.

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.

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.

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.

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.

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 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 luxury resort in Argentina, a Greek palace above a Mexican city and a former hotel in Hawaii.

Exploring a picturesque French castle, the ruins of a Kansas City hospital, an ancient Turkish city, and an island in Ireland that brought its inhabitants closer to God.

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.

The Tunnels of Gibraltar were a Second World War espionage base, hidden in the Rock of Gibraltar, which lay undiscovered for decades. At Atlas-1 Test Site, are the remains of an ingenious US Airforce project that continues to keep people safe.

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 Serbia, Fort Pike in Louisiana, and a mountainside refuge in Georgia that was revealed to the world by an act of God.

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

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

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

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 Camp Hero in Long Island, and a salt mine in Poland.

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.

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 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.