An underground city of salt.

An Austrian house of bones filled with hundreds of intricately painted skulls.

The fairy tale castle of the “fairy-tale king,” this was also the inspiration for Disney’s “Sleeping Beauty.”

Op-art architecture designed for happiness.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Macabre astrological automaton clock dating to the late 1400s.

Looming communist pillar with a Czech twist.

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.

Two stunning 17th-century libraries and a cabinet of curiosities.

Metro station with a claim to rock n' roll fame.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

20-foot tall lamp mumbles Swedish to celebrate the holidays.

Swedish skyscraper with a 90° twist.

Copenhagen's celebrated theme park and gardens.

Old Danish castle immortalized in Shakespeare's Hamlet.

Micro-nation based around a nine-story high illegally built tower.

A Very Low Frequency transmitter you can tune in on your PC.

A Gothic-inspired fish market is Gothenburg's best place to find loaves and fishes.

It houses the remains of a 17th-century version of the Titanic.

Vortex-shaped aquarium hosts Europe's largest school of piranhas and other ocean creatures.

A church of bones, decorated with 40,000 human skeletons.