One man's ambition created this psychedelic log home.

An artificial hill and apparent calendric structure built in the Early Middle Ages immortalizes a legendary Polish princess.

There are hundreds of secret WWII bases hidden in British forests. Built to fight a Nazi invasion, they remained unknown for decades.

For a brief time in 1960s France, families could climb into a tiny submarine and be pulled along an underwater journey.

A 90-year-old underground water reservoir offers a more industrial kind of tranquility.

Built following the War of 1812, this fort has withstood hurricanes for centuries.

This road in the Great Smoky Mountains was supposed to assuage a displaced community, but ended up a $52 million dead end.

The only runway directly into the magic kingdom has been closed since 1972, but it still sings to you if you drive fast enough.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

The ruins of an Estonian prison are drowning in the quarry lake where the convicts were once forced to work.

Vortex-shaped aquarium hosts Europe's largest school of piranhas and other ocean creatures.

The remains of a monument in the remote Kazakhstani desert dedicated to the only men to die in outer space, the crew of the Soyuz 11 rocket.

The 1936 Summer Olympics site is a crumbling remnant of sportsmanship and a history its host country would like to forget.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

An ancient tunnel in Jerusalem built to redirect water in the event of a siege is one of history’s great architectural innovations.

A late sculptor's last project was to turn this abandoned cement factory into a castle-themed amusement park.

This concrete ship has had four careers - World War I tanker, floating amusement park, fishing pier, and artificial reef.

This former quarry is now a picturesque gorge that hides a sunken lake.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

Dr. Strangelove-esque tours reveal the inside a bunker once reserved for Stalin himself.

This hauntingly stark structure is a relic of an industrial past.

Once the "Eighth Wonder of the World," this iron railroad bridge was decimated by a tornado.

This half-finished "city of toys" was almost Italy's own Las Vegas.

Derelict chemical plant on the North Sea is a beautiful industrial ruin.