A surreal museum of extraordinary industrial objects.

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

A crumbling World War I fort that is reached through a series of concrete tunnels.

The "dragon babies" of southeastern Europe.

This one-time health resort was used by aristocrats around the world.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

This huge metal monument is slowly being stripped to its concrete skeleton.

The remains of a sunken military ship wreck visible through clear water.

Legend has it fairies gathered at the site of this medieval castle.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

As can be expected from a centuries old church built in a canal city, the undercroft of this house of worship is beautifully flooded.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

The final resting place of the poets Shelley and Keats.

Sitting on an Italian hilltop is this surreal fortress built by the mad inventor of electrohomeopathy.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

According to the local folklore, the myriad colors of this lake are the result of a lovelorn wizard's blunder.

Stalactites and stalagmites in a beautifully lit cave.

Pompeii's less famous neighbor is still revealing her secrets.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.