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

Solar observatory doubles as a daring display of Expressionist architecture, much to Einstein's chagrin.

A quaint Russian village in the middle of a German metropolis.

The most visited, and possibly most controversial, museum in Germany.

Home to 10,000 medical specimens including the remains of Rudolf Virchow's extensive collection of pathological specimens.

A 12th-century fortress containing some of Berlin's oldest buildings.

When German-Iraqi relations broke down, this embassy was vacated post haste.

The music is over at the Ballhaus Riviera Ballroom, but the ballroom remains in haunting disrepair.

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.

Museum dedicated to literary greats of the Romantic Period is also the home in which Keats met his untimely end.

An alchemist's "magic door" stands in the middle of a Roman park.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

At the crypt of St. Mary of Eulogies and the Dead you are left alone to ponder mortality among piles of skulls.

One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.

Berlin's oldest surviving academic architecture hosted decades of animal dissections.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

Beneath the impressive baroque cathedral that rises from the center of Berlin lies the largest collection of Prussian royals in the world.

An eerie, derelict amusement park in Berlin.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

A medical facility that has been kept frozen in time.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

Collection of skeletal systems from the "world's leading supplier of osteological specimens."