Stunning Roman aqueduct used for 1900 years and still standing.

World's first "penitentiary," meant to be humane, drove men insane.

Commemorating the spot where the famous scientist fed his pigeons.

This historic, palatial theater is now one of the world’s most beautiful bookstores.

A gleaming white and undulating tower marks the border between Georgia and Turkey.

A Museum of Holography frozen in 1974.

Ruins of a late 1950s Polish ski jump ramp in the middle of the city.

The taxidermied remains of the "last wild grizzly bear in California" and of the symbol of the state of California.

Rusting ships sit in a desert where a sea used to be.

A geological bull's-eye visible from outer space.

Cavernous opening completely encased in Karst limestone.

England's most notorious suicide spot.

Mural made of 100,000 pieces of hand blown glass, and until recently, the largest glass mural in the US.

340 bicycles, 65 feet high.

270 million year-old forest of stone.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

This dramatic sea spire is home to the world's rarest insect and is part of the lost continent of Zealandia.

Mysterious craters may have been home to an ancient cult.

Tiny Swedish village with a distinct local phenomenon known as an "Elk Shower."

Britain's oldest and biggest hole in the ground.

A neutrino detector built into the largest man-made underground cavity in the world.

An ancient Thracian city where fire rituals were practiced on the largest cult altar in Southeast Europe.