Abandoned railway line circling the city of Paris.

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.

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

On the coast of Sardinia, a once-great mining village is finding new life as a coastal resort town.

Stalactites and stalagmites in a beautifully lit cave.

The titular "little arch" near this Italian resort is one of the most popular diving spots in the country.

This elaborate hole in the ground was built as a sacred site for an ancient civilization.

Ancient cave tombs known as the "houses of fairies."

This one-of-a-kind archeological site is home to strange prehistoric ruins, the original use of which is still a mystery.

Architecturally stunning library serves as the hub of Finnish scholarly life and culture.

An alien church provides much needed silence in the midst of a Finland shopping center.

A subterranean house of worship carved right out of the bedrock.

An old asylum graveyard that's been abandoned for half a century attracts those seeking a dark thrill.

A Jenga-style cylindrical tower of books that appears to go on forever.

Countless grotesque faces stare out from this eerie Prague art wall.

The history of occult science is turned into a creepshow at this lurid Prague tourist attraction.

A self-proclaimed libertarian micro-state on a tiny bit of disputed territory between Serbia and Croatia.

This former abandoned hospital, a complex of stunning 19th century buildings, once housed 2,000 psychiatric patients.

An avant-garde artist is survived by his seaside garden.

A house of bones — but nobody is quite sure to whom they belong.

This oak sculpture at the edge of a small woodland is nine feet tall and shrouded in mystery.

Huge concrete structures designed as an early warning system for Britain to detect enemy aircraft.

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

Angels, demons, and tortured souls on a giant wall mural in a little church.