Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

The skulls and bones of thousands of soldiers line the walls of this small Italian chapel.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

The plague quarantine island home to the alleged "Vampire of Venice."

A small island less than half a mile from Venice is a forbidden island with a dark and twisted past.

The oldest of Venice's plague quarantine stations, designed to keep the medieval city safe from disease.

Venice's "Island of the Mad."

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

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

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

Each year, Germany's "City of Dragons" slays the world's largest walking robot.

Ruins of a German Castle on top of a towering stone pillar.

A small man-controlled waterfall powers an Art Nouveau elevator and is accessed via narrow gauge, solar-powered tramway.

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

What looks like a suicide in progress is actually a statue of Sigmund Freud.

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

Underneath the city that invented pilsners are a series of historic tunnels that have been storing beer for centuries.

The mystery of the Putim Ossuary involves a tricorn hat.

Underneath this small church are 15,000 bones, arranged by an obsessive academic.

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

A crucified and bearded female saint.

A 400-year-old mummified arm dangles from the ceiling of St. James the Greater, serving as a warning to thieves.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.