Empty buildings and infrastructures are full of the echoes of real people and vanished lives, leaving many questions unanswered and mysteries unsolved. We explore the worlds strangest engineering projects that created empty silent cities. We ask why a ruined cold war air base has become a no-go area and how a tiny Japanese mining island become the most over-crowded place on the planet. We find out if the street layout of the Soviet Union's model city become a matter of life or death for its population. And how did Nazi Germany create a huge mind control facility at a holiday resort?

We aim for the stars and find out why unwanted battleship guns allow the United States to gain vital information about the borders of space. We ask how the shattered remains of a secret Nazi base became the first on the path to a new world, with the development of the ground-breaking V2 rocket. We explore a forgotten structure deep in the Arizona desert to ask if it is the true home of America's space programme. And we reveal the bizarre link between a discarded oil drum and a Cold War struggle to survive in zero gravity.

Soaring across some of the widest rivers and deepest valleys on the planet, bridges have always been at the cutting edge of engineering. We travel high into the mountains of the Colorado desert to find out why a hidden engineering masterpiece could disappear at any time. We ask why a stretch of overgrown concrete in a Czech reservoir is known as 'Hitler's bridge'. We find out how the highest bridge in the world collapsed in less than one minute. Finally, we uncover the story behind Cape Town's invisible bridge, which never carried a single vehicle.

Exploring ship graveyards, including Scapa Flow in Orkney, where German warships were scuttled after the First World War, and Mallows Bay, home to 200 wrecks colonised by wildlife.

How Europe's most advanced power station became a film set. Plus, the structures made by scientific pioneer Nikola Tesla in his thwarted quest to prove the US with free electricity.

Hear how a crumbling hill in the Peak District and dunes in California caused the closure of two roads. Learn why a route used by the French Resistance shut in 2003.

A dark past explains why the Pölitz Synthetic Fuel Plant in Northern Poland is now a derelict industrial site littered with tunnels, bunkers and huge crumbling concrete structures lost in dense forest. The site was built in 1937 as part of Nazi Germany's drive to become self-sufficient on fuel, but it was no ordinary refinery. It used the latest technology at the time, at great expense, to turn coal into oil. In 1945 an Allied air raid pulverised the plant, severely wounding the German war machine and leaving the site in ruins.

Other structures examined in the first episode include the incredible vertical Phoenix Shot Tower in Baltimore, which was built to provide America's own ammunition, the former American spy instillation called Teufelsberg (or "Devil's Mountain") in Berlin which waged the Cold War against the Soviet Union, and the now derelict Rubjerg Knude Lighthouse which was built on Europe's second-fastest moving sand dune in Denmark.

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.

An abandoned concrete wall... five strange deserted structures. A lost escape route from nuclear Armageddon... A submerged link to D-day... Once they were at the cutting edge of design and construction, now they lie disused, contaminated and dangerous. But who built them? And why were they abandoned?

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?

The Georg Thiele was a technological masterpiece, but it is a shipwreck, lost to the sea in a Norwegian Fjord after running aground during a naval battle in WWII.

Also in this episode, a mysterious concrete giant which echoes the Communist era atop a mountain peak in Bulgaria, a fantastical structure built in the middle of an American river, and one of the world's first and finest Artic feats of engineering, The Miles Glacier Bridge in Alaska, which, when it was first built in the early 1900s, was known as the Million Dollar Bridge.

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?

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 towering structure with an explosive past, a deserted cityscape, a mysterious top-secret facility and a vast Nazi construction.

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.

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.

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 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.

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.

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.

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

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

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.

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