This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

An artsy hidden staircase leads to breathtaking views of San Francisco.

A huge musical instrument played by the ocean.

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

Legends of treasure and spirits flow from this this fairy tale-like oasis.

This 600-year-old home seems to defy physics.

A beautiful maze marks where three countries meet.

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

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

You haven’t properly toured a winery until you’ve slept in an actual wine barrel.

An elegant chandelier hangs over this ancient sewer chamber, now open for concerts and public tours.

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

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.

The highest point in Belgium is a staircase to nowhere.

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

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

Thousands of flowers create enchanting pink tunnels over the city streets.

A Neolithic burial site erected around 3000 BC.

It has an American Dream Car exhibit, Europe's largest Formula One collection, and many, many mannequins.

Every half hour the eye-rolling clock face sticks out its tongue to mock the good citizens of Koblenz.

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

Crop circles inspired this whimsical garden in Germany.

This unique Renaissance castle was turned into a home for Nazi occultism.