Living trees form the structure of an open-air palace.

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

Ruins of a German Castle on top of a towering stone pillar.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

The birthplace of an eccentric alchemist and possible inspiration for the fictional reanimator of monsters.

The fairy tale castle of the "fairy-tale king."

A hands-off space for graffiti artists to hone and display their skills.

Since 1874, this macabre collection has developed into a museum devoted to Scotland Yard's mementos of dastardly deeds.

The largest of London's subterranean rivers and once a mad, bad center of London life.

Executed in 1401, Exhumed in 1878, Stolen in 2010.

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

A magical and peaceful ruined Cistercian abbey in what is now southern Belgium.

Lavish royal estate punctuated with heated greenhouses.

The tallest waterfall in the Netherlands is a lovely, stepped feature that is only 50 feet tall.

This small electronics museum is full of whirring, humming, clicking ephemera.

From Tintin to the Smurfs, Europe's greatest graphic icons are celebrated in a grand Art Noveau gallery.

Dummies recreate radiological discoveries from history.

Museum covers every step of the chocolate-making process, from cultivation to the finished product.

A 12th-century fortress containing some of Berlin's oldest buildings.

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

A museum dedicated to a Cold War era sausage.

An old department store turned Nazi prison turned artist commune.

Two monstrous faces loom over a village in Czechia.

A former squatter's paradise outside Prague.