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.

Including an exploration of a marooned iron-clad structure in Portland, off the coast of England, that hides a dramatic story of war and resilience; Pratt Cotton Gin Mill, a vast facility in the heart of America's deep south that helped tear apart a nation; and a Mediterranean island fortress at Spinalonga, Greece, that became the scene of a dark conspiracy.

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 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 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.

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.

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

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

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

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

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.

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

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

Exploring Old Byron Hot Springs in the Californian desert - a once glittering Hollywood hotspot, converted into a top-secret interrogation centre.

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

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

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.

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.

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