The stones of this Incan wall complex fit together so well you couldn't fit a piece of paper between some of them.

This colossal war machine is now a living museum dedicated to underwater warfare.

A former copper mine which became a truly unsuccessful prison.

This hospital once pioneered the use of electroencephalograms, but fell into maltreatment, abuse, and eventual abandonment.

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

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

America's post-nuclear-attack chambers of Congress.

Few other hotels can rival the grandeur of the Castle in the Rockies.

Costa Rican accommodation resembles a crash site, but with a nice balcony.

Luxurious hotel designed to stir the imagination of its many visitors.

This hospital fell into ruins after failing to act as the advocate for the mentally ill it was designed to be.

In the middle of downtown Brooklyn lies a 165 year old secret hidden right below the surface (closed to the public indefinitely).

An Irish cemetery filled with victims of political strife and violent conflict, including the grave of Bobby Sands.

The oldest steel ship in Iceland has been beached for years and is now a rusting ruin.

This small Irish village suffered the greatest loss of life when the Titanic sank.

The world's largest ship graveyard is the product of decades of corruption.

Dedicated to the art and science of glass in equal measure, this space is as much laboratory as museum.

Temples adorned with intricate, erotic sculptures make up one of the "seven wonders" of India.

Hundreds of antique bank vault locks on display in New York City.

Longest road tunnel in the world features an air treatment plant and the illusion of daylight.

This little museum is built on a theater that was once a wildly elaborate speakeasy.

This trio of Australian rock spires may have inspired aboriginal legend or just modern tourism.

Everyone from Mark Twain to Teddy Roosevelt has a pipe hanging from the walls of this historic chophouse.

This former Masonic hall has been turned into an art project that uses even more metaphysical iconography.