This overgrown mountain village has been abandoned for nearly a century.

A star-shaped fortress town fort built in the geometric model of the Renaissance utopian city.

One of the largest caves in the world open to the public.

During World War II, this rice mill became a Nazi concentration camp.

A whimsical bridge adorned with decorative dragons.

Martin Bricelj Baraga's monolithic sculpture measures the blueness of the sky, and changes color to match it.

This massive subterranean fissure is known as the "underground Grand Canyon."

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

This one-time health resort was used by aristocrats around the world.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

The abandoned military base looks like a post-apocalyptic wasteland.

A collection of intricate sculptures so small they have to be seen through a microscope.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

Poland's oldest salt mine has nearly everything one needs to live underground forever.

The 700-year-old fortress was the site of Count Orlok's castle in "Nosferatu."

Abandoned railway line circling the city of Paris.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Is it an island or a volcano? That question probably explains why it's uninhabited.

An abandoned 14th-century castle and prison complex on a small island in the Neva River.

The largest Buddhist city in Europe is a haven for chess fanatics.

An unused hyberbolic electricity pylon kept as architectural monument.

Fascinating early attempt at a Jewish autonomous settlement.

Ukrainian defense contractor's center for studying "pyramid energy."