A beautiful but toxic fountain of mercury.

Browse through a century of this principality's first popular export.

Walk inside a half mile long crevice right outside the town of Garmisch Partenkirchen.

The prison where Hitler wrote "Mein Kampf," and 278 Nazis were later executed for war crimes.

Hidden in the forest are the crumbling, graffiti-covered remains of the factory where most of Germany's explosives were produced during World War II.

Two unremarkable-looking rocks on a cobblestone street are actually ancient wanderers; one a 150-million-year-old limestone, the other a 1.8-billion-year-old granite.

Vienna's diversity-themed traffic lights were inspired by the Eurovision Song Contest.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

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

A fire once nearly devoured this gorgeous 14th-century Gothic cathedral.

This elaborately decorated, fairytale-like Romanian royal palace is one of the most striking castles in Europe.

The once forbidden "secret cabinet" of erotic art from excavations of Pompeii and Herculaneum.

Erotic art covers the walls of the largest ancient pleasure palace.

This enormous abandoned factory is now a makeshift graffiti gallery.

Yale University's home for rare works, including the mysterious Voynich Manuscript.

This old cement mine has been used as everything from a mushroom farm to a recording studio.

A ruined mansion hidden in the woods of the Hudson Valley, home of a tragically doomed romance.

This stunning iron gate designed by Modernist architect Antoni Gaudí is filled with mythic symbolism.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

A fascist-era rural village abandoned since the early 1980s.

Ghost Town in the Demilitarized Zone of the Golan Heights.

This small town in the Netherlands has no roads but instead, miles of canals and over 100 bridges.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.