This overgrown Illinois water park offers a whole new type of adventure.

World's second largest particle accelerator, where nature reveals its secrets.

A living snapshot of a different time in America is preserved and maintained by a community of volunteers.

It was originally part of a "terrible lizards" collection at the 1964 New York World’s Fair.

The longest navigable underground river in the United States is home to countless blind and albino animals.

The scuba diving training facility was named for the steam that rises from the cave's chimney.

Less a museum than a bizarre fantasy world created by artists and engineers.

A gem in the small Missouri town where Winston Churchill coined the term "Iron Curtain" and effectively began the Cold War.

Curious cave that stays a cool 56 degrees all year long.

A cave 150 feet beneath Kansas City is the perfect climate for growing 10,000 delicate orchids.

This empty Detroit high school was too expensive to maintain or destroy.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

An old soap company building now houses one of Minneapolis’s oldest independent non-profit art galleries.

The city is full of whimsical portals to another world.

An old spiral fire escape dangles above a public courtyard in Midtown Oklahoma City.

"They died with their boots on."

Astounding collection of coin-operated games and automata.

The saga of the massive nut begins and ends in Texas.