The most visited, and possibly most controversial, museum in Germany.

What started as a tongue-in-cheek shrine is now a full-blown museum celebrating "The Hoff" and his longtime love affair with Berlin.

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

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

The room where Vincent van Gogh died.

The artist and his brother are buried in a landscape straight out of a van Gogh painting.

The only remaining collection of flayed figures made by French "madman" Honoré Fragonard.

A charming flea market shop dedicated to retrofuturistic apparati.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

The history of radiation is on safe display at the foot of a radiation science laboratory.

19th century pendulum and a clock restored by a rogue group of guerilla artists.

This massive library holds what was once the largest book collection in the world.

A curious collection of locks and keys.

France's national museum of scientific and industrial instruments.

A mechanized clock where a man fights off a dragon, crab, and rooster.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

This peculiar museum offers hands-on interaction with seemingly intangible principles of mathematics.

The prototype for all Nazi concentration camps.

Four-story slides send people whizzing through the math department at this Munich university.

This fairy-tale castle would make Dracula (who is said to have been imprisoned there) jealous.

Two monstrous faces loom over a village in Czechia.

Two stunning 17th-century libraries and a cabinet of curiosities.