The ruins of this medieval castle on a foggy hill tell the story of a once-mighty empire.

Here, cows that make vodka are treated like celebrities.

Rumors of the occult haunt this upscale 1920s hotel.

The medieval legend behind this holy well was one of the inspirations behind "Alice's Adventures in Wonderland."

Moscow's imposing monument to the Space Age.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

Dr. Strangelove-esque tours reveal the inside a bunker once reserved for Stalin himself.

The gorgeous entrances into the city's underbelly look more like grand halls than subway stops.

For those going through a life transition, a place to leave behind a piece of your former self.

In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

One of the oldest seagoing boats in the world can be found at the Dover Museum.

An elegant chandelier hangs over this ancient sewer chamber, now open for concerts and public tours.

A church filled with the bones of hundreds of virgins martyrs—or so they say.

Europe's official "zero-level," the equator of elevation.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

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

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A neighborhood park in the city of Cáceres hides what some believe are revolutionary examples of Neanderthal cave art.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

A massive work of modern art that appears to be a crop circle in the middle of the desert.

Conspiracy theories and occult legends surround this mysterious natural rock formation.

Double spiral staircases are not unheard of, but they are very rare.

Climb to the top of its spiral spire for spectacular views of Copenhagen.

This volcano rises like a giant anthill from the plains below, with a road spiraling up to the rim.