Curious onlookers have suspected this strange structure is a secret government base.

The bank's whimsical shape was inspired by a child’s toy.

The massive steel ring looks like it could be China’s first Stargate.

These Nubian pyramids are strange and unique, even by pyramid standards.

Remains of an abandoned coral city.

This off-limits room in the National Library of France is home to a system of pneumatic tubes, once used to bring books to readers.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

This Parisian fountain is a little bit fantasy and a little bit nightclub.

A subterranean shelter remains intact under a busy Paris railway station.

A surrealist timepiece by the artist of melting clocks.

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

"Drunken ship" sculpture memorializing the French poet in the city where he died.

A crumbling island fortress that seems to be covered in a field of stone crosses but is simply incomplete.

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

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

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

The site of good faith and good nature in the fictional world of Kcymaerxthaere.

One of the world's heaviest musical instruments towers within a popular urban park.

Metro station with a claim to rock n' roll fame.

This conical hill was built as a testing ground for an engineer known as the Glider King.

An eerie, derelict amusement park in Berlin.

A tree-like building perches on its trunk in the Steglitz neighborhood of Berlin.

Someone loved this song enough to carve all of its lyrics onto a tree trunk in a Berlin park.