The world's longest known cave system.

A bizarre house filled with an astounding array of collections.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A museum dedicated to the alleged Roswell Incident.

A gorgeous garden oasis with winding paths, stone bridges, and a troubling history.

Abandoned railroad tunnel is home to a colony of three million Mexican free-tail bats.

A Hawaiian stairway to heaven—that you can't climb.

This narrow coastline trail through the dense Kauai wilderness is among the most beautiful and dangerous in the world.

This lighthouse and shipwreck museum keep a torch burning for the memory of the SS Edmund Fitzgerald.

Island where motor vehicles are banned -- home to the only carless highway in the United States.

Strange physical sensations and optical contradictions keep visitors coming back for more.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.

One of the largest crucifixes in the world stands 55 feet tall in a secluded, wooded area of northern Michigan.

This national park on the shore of Lake Michigan features remarkable dunes that lie at the heart of a Chippewa legend.

World's largest Christmas store.

What was once the largest NFL stadium.

Hell on Earth is actually a small town in Michigan where anyone can be mayor for a day.

Largest tulip festival in America, includes fireworks, a parade, and a carnival.

The Bucyrus-Erie model 1850B electric shovel, or "Big Brutus," the largest existing electric shovel in the world.

The inventor of a number of hybrid corn species is immortalized with a field of giant corn.

Cleveland's giant "free" stamp is a nod to the Civil War, but was misinterpreted for years.

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

Small plaque marks the spot, but the true center is located about half a mile away on a private pig farm.

Massive still life just off the highway in Kansas.