A psychedelic labyrinth on the San Francisco bay.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

These crumbling Nazi artillery bunkers are now fair game for massive graffiti projects.

An aluminum skeleton brings Chinese mythology to the French shore.

The largest underground church in Europe.

This natural French spring has been turned into a magical grotto by Roman and medieval constructions.

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

This French ghost town from World War II has been left as a memorial to German atrocities during World War II.

France's most famous cemetery, with some of its most curious tombs.

Abandoned railway line circling the city of Paris.

Paris' linguistic guide to the international language of, yes, love.

The world's greatest slide descends 18 stories from this looping mountaintop viewing platform.

A monument to the man who almost killed Hitler.

The ruined remains of the airport Claus von Stauffenberg departed in his failed attempt to kill Adolf Hitler.

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

A restaurant and observation deck built in a unique broadcasting antenna.

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

A stairway to heaven, or to nowhere at all.

Hitler's bleak vision of relaxation still stands as a mostly abandoned 10,000-room resort complex.

A German apartment building hosting as many trees as human occupants.

Gardens representing parts of Asia, Europe, and the Mid East are tucked away among the Soviet-style buildings in East Berlin.

When the rain falls, this drain system turns into a musical instrument.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

Art and a pun, all in one.