Floating swimming pool within a moored vessel.

An eerie, derelict amusement park in Berlin.

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

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

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

This strange building looks like a medieval fortress crashed into a 1960s Brutalist office block.

These little castles each held thousands of pigeons.

17th century mosque for Shah Abbas' harem.

Named after a legendary garden called Eram in southern Arabia, built by order of Shaddad, an Arab king who wanted to compete with Paradise.

Mirrors and glass shards cover every inch of this arrestingly beautiful mosque.

This beautiful system of tunnels built into natural rock serves as a centuries old plumbing system.

The ancient necropolis houses the immense rock-cut tombs of four Persian kings.

Graffiti covers the walls of a room where university students through the centuries have waited nervously to defend their theses.

A 'living museum' in Leiden, the oldest of its kind in the Netherlands.

This historic Dutch newspaper building is covered with media-themed details—and one unrelated oddity.

This enormous storm barrier is one of the largest moving structures on Earth, with each arm taller than the Washington Monument.

The world's first interactive human body museum also serves as a chair for a giant orange man.

Now a museum, this building was once a 14th-century monastery and the place where the founder of the Dutch nation lived and was assassinated.

Hidden within a Netherlands crater is a stone bed that lets those who lie in it see the sky as a curved surface.

Survival capsules find a second life as a unique hotel.

A miniature city, once ruled by the Queen of the Netherlands.

A preserved building where the dead were once watched for signs of life.

A seven-century-old jail tells a not-so-pleasant history of crime and punishment.

The largest 19th century panorama in the world still in-situ.