A spiral staircase twists to the top of this unusual Czech lookout tower.

This former quarry is now a picturesque gorge that hides a sunken lake.

An eerie, existential museum dedicated to the author of "The Metamorphosis."

The tunnel's elegant proportions keep you snug with no claustrophobia freak-out.

A mocking tribute to the past and modern leadership of Prague.

A bust of Franz Kafka spins in pieces, reflecting the writer's inner torment.

Countless grotesque faces stare out from this eerie Prague art wall.

The hidden lair of an alchemist rediscovered in a 2002 flood.

A Jenga-style cylindrical tower of books that appears to go on forever.

An eclectic art form practiced by untrained masters is celebrated at this museum in the heart of Zagreb's old Upper Town.

This 170-year-old Swiss guesthouse built into the side of a mountain is best accessed by a cable car.

An abandoned railroad tunnel is now filled with bioluminescent bugs.

A former chicken restaurant that doubled as a speakeasy is now a quirky home full of wonderfully strange traditions.

The world's first hotel built in an abandoned water-filled quarry.

This hulking behemoth is actually five interconnected towers built in the 1960s.

This curious building hides eclectic details like medieval gargoyles alongside naked angels and Art Nouveau mosaics.

A museum built around a bus-sized fossil on the side of the highway.

A three-tiered waterfall plummets from a mountain cave with amazing views over the countryside.

Largest monument in Colombia depicts 14 lancers who drove back an army.

Colorful lights and mirror-like brine pools create trippy illusions within the historic mine.

This whimsical home made entirely from clay is basically a giant piece of pottery.

Reproductions of nine banned oil paintings coyly hidden behind a curtain in a New Mexico conference room.

It's hard to believe the dizzying patterns covering this abandoned mine are completely natural.

Pompeii's less famous neighbor is still revealing her secrets.