Peek into a cave of giant, glimmering crystals.

Where lovers tie birch branches into long-lived knots.

An unrealized dream to wirelessly electrify the entire Earth.

Covered in tens of thousands of coats of paint, this Indiana attraction holds a world record all its own.

Catalonia Tradition: Beating the hollow Christmas log until it defecates in your fireplace.

An abandoned train station in Munich constructed for the 1972 Olympic games.

The portrait of a man from Japan who sent weekly letters to a Dutch hotel he never visited.

A boulder in the Churchyard of Down Cathedral marks the legendary burial place of "The Apostle of Ireland."

Hundreds of glow-in-the-dark objects light up a museum in a historic zinc mine.

This decommissioned nuclear power plant offers tours of its Communist-era control room and reactor hall.

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

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

This bunker in northern France was built by Nazi German forces with the intention of launching up to 50 V2 rockets at London each day.

This fountain tucked away in a park is the focal point of the only "Green Basilica" in Germany.

This famed marionette theater and museum is bursting with imaginative string puppets.

Walk inside a half mile long crevice right outside the town of Garmisch Partenkirchen.

Small museum dedicated to one of the founding fathers of modern astronautics.

The Arctic Archipelago is home to world's largest third order island: an island in a lake on an island in a lake on an island.

This museum of Viking vessels allows visitors to take a replica out for a spin.

An important piece of history from mankind's journey to the moon sits in the lobby of a government science lab.

An impressive array of unique homemade planetariums.

Inside the dome of this gigantic, Saturn-shaped building is one of the largest planetariums in Asia.

A wonderfully strange collection of 500+ stuffed frogs doing people things.

A popular 19th-century natural landmark is now hidden within a sprawling forest.