The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

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

A former squatter's paradise outside Prague.

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

This automated sculpture of two men peeing will spell out text messages with their micturition.

Street artists transformed an abandoned air vent into the beloved Star Wars robot.

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

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

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

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

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

These former Nazi anti-aircraft towers offer a singular view of the north of Berlin in the summer, and a sanctuary for bats in winter.

This Berlin island is home to a flock of free-roaming peacocks, as well as a historic ivory folly.

An abandoned NSA listening post on Berlin's "Devil's Mountain."

An eerie, derelict amusement park in Berlin.

One of the most easily accessible examples of the rare 1960s UFO houses.

Tirelessly maintained by a Wisconsin man named JFK.

A unique botanical garden housed in three giant geodesic domes.

These Great Lakes sea caves accessible by boat in the summer turn into temples of ice reachable by foot in the winter.

"Portugal's Stonehenge" is made up of nut-like stones aligned with the heavens.

This crumbling Portuguese ruin overlooks the populace it once ruled.

This abandoned five-star hotel is now a five-star urban exploration destination.

An abandoned mine now resembles a post-apocalyptic landscape of derelict buildings and blood-red pools of water.

This gaping hole in the middle of a remote mountain lake looks like a portal to another dimension.