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

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Every equinox this Maya pyramid puts on a spooky ancient light show.

An ancient system of freshwater caves filled with animal bones, including that of species long-extinct.

A flooded Mexican cave that hides a river beneath the water.

A cave dug by a man directed by ghosts to find pirate treasure.

Palatial mansion estate used in films including "Flowers in the Attic" and "The Witches of Eastwick."

An eccentric inventor's castle home with its own indoor weather system.

Experience the hysteria of a 17th century witch hunt through goofy reenactments and wax dummies that should probably be burned at the stake.

"Try not to knock anything over!"

The only structure left with direct ties to the Salem witchcraft trials of 1692.

Ugly 18th-century dwarf statues living in a perfectly landscaped Austrian garden.

Dress up like a miner and take a slide into the disco-lit depths of this once foundational salt mine.

Originally envisioned by King Ludwig II to rival Versailles, Herrenchiemsee's "New Palace" remains half-gilded for lack of funds.

Soaring over 6,000 feet in the Bavarian Alps, this beer garden was once Hitler's 50th birthday present.

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

The only museum with its curator—and her pets—buried inside.

100 year tradition of fist fights, marked by marble footsteps.

Go inside to really appreciate this 500-year-old technological masterpiece.

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

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

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

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