The attic of a four-century-old canal house hides a clandestine church.

A poignant mural honors the heroic teenage non-conformists who took on the Nazis and paid the ultimate price.

Gargoyle head that brings good luck.

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

This stunning, out-of-the-way Croatian monument commemorates a community's uprising against occupying fascist forces.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

Yugoslavia's biggest underground airport lies in ruins.

An unsettling sculpture of a boy hanging out in a street in Ghent has been baffling visitors for years.

Sculpture designed by Turkish artist and professor Mehmet Ali Uysal.

This collection of lurid religious statues tell the tales of a saint who stood down the devil.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

This collection of solar timekeepers includes the world's first digital sundial.

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

The footprint of a frustrated devil in Munich's Cathedral.

Daily jousts and dancing barrel makers in Munich's mechanical clock.

After years of being casually peed on by humans, this tree is peeing back.

You would never come across this tiny green oasis if you didn't know it existed.

A floating cat sanctuary on an Amsterdam canal.

In addition to fine dairy products, the world's most beautiful milk shop also offers a feast for the eyes.

The remnants of a WWI naval mine that once terrorized the country now decorates a street.

A market built atop boats is one of the few floating holiday markets in Europe.

A 19th-century subterranean reservoir repurposed as a contemporary art cave.

The Swiss artist's bulbous and overgrown shape-shifting sculpture controversially graces the center of Bern.

A long spiraling walkway winds through the woods, and around a copper beech tree at the center.