This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.

A surreal museum of extraordinary industrial objects.

A former top secret nuclear fallout shelter now operates like a hotel stuck in the Cold War.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

Mummified monks and the accidentally interred, in a 17th-century crypt.

A museum of alchemy and a basement laboratory all housed in an ancient building in a Gothic tower.

One man's personal collection of KGB memorabilia is presented along with his strange viewpoint.

A spiral staircase twists to the top of this unusual Czech lookout tower.

Europe's second largest ossuary wasn't discovered until 2001.

Underneath this small church are 15,000 bones, arranged by an obsessive academic.

This doorless 20th-century elevator doesn't stop or slow down.

An eerie, existential museum dedicated to the author of "The Metamorphosis."

Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.

A steampunk-styled three-floor factory churning out art, activism, and electronic beats.

The first museum in the world devoted to sexual gadgetry.

Walk through Czech history in Prague's largest graveyard.

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

The hidden lair of an alchemist rediscovered in a 2002 flood.

A church of bones, decorated with 40,000 human skeletons.

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