Site of one of World War I's most horrific scenes.

The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

A striking 12th-century-style castle built on the edge of a cliff.

The abandoned mine where American troops discovered a treasure trove of art and artifacts hidden by the Nazis.

The great Danube river starts here.

A church filled with the bones of hundreds of virgins martyrs—or so they say.

A beautiful maze marks where three countries meet.

Final resting place of the humble physicist who discovered X-rays, and made the invisible visible.

Statue of a decomposing prince that once held his heart in its hand.

Hiding the longest subterranean river known in the world.

A Neolithic burial site erected around 3000 BC.

This striking fort on the Maginot Line looks just as it did after being destroyed in the Fall of France.

A Black Forest cuckoo clock theme park features one timepiece big enough to walk inside.

This former Nazi castle was built as a school to train what would have been the future of the Third Reich.

The birthplace of the builder of the Statue of Liberty is now a museum dedicated to his work.

This unusual piece of Renaissance art depicting the bodily horror of crucifixion and skin disease may have been inspired by fungus-induced hallucinations.

This old wooden funicular railway leads to a cemetery in the forest.

An ancient monastery, a locked room, and a mysterious book heist.

This ancient ruined monastery has been destroyed by fire so many times that it seems like God hates it.

Carved fountains poignantly placed in parks and in front of special monuments.

The sweet story of how American cargo planes became known as "Candy Bombers" during the Berlin Blockade.

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

This noble mash-up in eastern Luxembourg is part Medieval, part Renaissance, all castle.

This tri-part waterfall is a little bit of fairytale beauty in the heart of Luxembourg's Little Switzerland.