Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

This dramatic landscape hidden on the Isle of Skye looks as though you've stepped into the magical realm.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

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

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

Electrical curiosity museum housed in an old transformer station.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

This off-beat, quirky communism-themed bar isn't afraid to poke fun at its history.

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

A museum in the childhood house of a medical pioneer.

A Hungarian pharmacy museum with a box full of mummy powder.

A series of caves under Castle Hill that once held the prisoner Vlad Tepes, better known as Count Dracula.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

One man's personal kunstkammer, museum and shop.

Housed in an old church, this hunting museum holds a collection of mythical bird-rabbit creatures.

The patron saint of spinsters grasps a container of dried blood.

Man-made cave with enigmatic carvings, some say made by the Knights Templar themselves.

This series of Scottish caves has no clear purpose other than baffling historians.

360° views of the city plus five floors of optical illusions and hands-on science.

This stately estate house features a tower covered in a bright, modern mural.

These mysterious religious carvings were once thought to be thousands of years old but are actually the work of modern eccentric.

The strange behavior of a tween led to allegations of witchcraft and a curse being placed on anybody within earshot.

The oldest house in Glasgow is now a museum dedicated to the city's medieval history.

The elaborate clockwork contraptions in this Scottish gallery create small worlds of whimsy and horror.