On Japan's Tashirojima Island, cats are king.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

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

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

This little-known relic crypt holds stolen parts of a Roman Empress.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

Possibly the world's largest hourglass only needs to be reset every New Year's Eve.

This quaint Hungarian railway system is operated exclusively by children between the ages of 10 and 14.

The Rozenberg wind wall in South Holland makes for smooth sailing through the Calandbrug canal.

This miniature take on the Kremlin is one Dutch man's retirement project.

The world's only museum devoted to the wonders of fluorescence.

The former home of a mad diplomat is said to still be marked in bloody, arcane scrawls.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

This historic Amsterdam bar used to accept sailor's monkeys as payment.

This unattributed sculpture in Amsterdam is hiding in plain sight.

This Budapest bar allows drinkers to leave their mark on the walls, floor, and even ceiling.

A museum dedicated to a secret military hospital hidden beneath a castle in Budapest.

Uh, pardon me, ma'am, but I couldn't help noticing that there's a Columbo statue in the middle of Budapest.

Electrical curiosity museum housed in an old transformer station.

A marvel of technology a century ago, this disused power station now offers a lovely glimpse into the industrial design of the past.

This hidden art nouveau gem was designed by an architect in search of a national style.

A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

The mummified right fist of a 1,000-year-old saint-king sits inside an ornate golden reliquary.