The only visible remains of this ancient Greek underground temple is its roof protruding from the earth.

Also known as the Temple of Poseidon, this is one of the best-preserved Greek temples in the world.

According to the legend, this structure was built in a single night with the help of the devil.

Ride a boat through this magnificent underground world, which now doubles as a theater.

A beautifully well-preserved ancient Roman villa.

Centuries of human activity have forged an eerie landscape of ruins and craters on an exposed and windswept hilltop.

A desert settlement founded and later abandoned by Hawaiian members of the Church of Jesus Christ of Latter-day Saints in Utah's Skull Valley.

Built by the patron saint of illusionists this Elizabethan manor house is riddled with secret cubbies for hiding priests.

The last occupied troglodyte dwellings in England weren't abandoned until the 1960s.

A cableway for car transport.

A mesmerizing landscape of 18th-century cellars carved out of the land.

This medieval settlement was abandoned after a series of landslides. What remained was largely destroyed during a mock battle for a WWII film reel.

A ruined castle stands atop a hill surrounded by dragon lore.

The site of many battles and tragedies, including the 40 maidens who leapt into the sea.

The stately remains of Llywelyn the Great's mighty fortress.

The blood-soaked ruins of the castle where the murderous Blood Countess was walled in alive.

A copy of the brutal decapitation device that predated the French Guillotine by about 200 years.

A mysterious bridge over a sunken Roman road.

This small primate research island is teeming with playing, fighting wild monkeys.

This tiny island is home to the world's largest colony of Northern gannets.

This abandoned artificial island off the coast of New York City is now home to dozens of harbor seals.

In paradise, feral pigs have claimed an island all to themselves.

A tiny village is home to the world's only diner completely devoted to the many varieties of traditional Swedish dumplings.

This ghost town houses the remains of Alabama's old state capital.