Tubing through a cave lit with glowworms is a magical underground experience.

A boat ride through utter darkness, lit only by headlamps, reveals an emerald green pool locals believe is sacred.

The world's longest known cave system.

Former self-sufficient mental institution now a planned community.

A popular place to pick up prehistoric coral fossils from the time when Michigan was an ocean.

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

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

Turnip-shaped island just off the Michigan shore in Lake Huron.

This Hawaiian cattle ranch acts as a museum devoted to the island cowboys that predate the wild west.

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

The southernmost point in the United States is a beautiful place to look at but a deadly place to wade in.

Submerged lava formations create incredible waterworks.

This former luxury resort in Kaua'i is now an abandoned relic.

A once-glowing grotto at the bottom of Waikapalae Wet Cave.

This industrial area was the dumping ground for massive amounts of trash, some of which washes up as tiny bits of sea glass.

A prehistoric landscape hidden in the cliffs of Maha'ulepu.

A series of waterfalls and pools that flow through the 'Ohe'o Gulch and into the ocean.

These picturesque Hawaiian falls are home to a rare species of fish that uses a special sucker to climb up cliffs.

Take a steam-powered ride straight out of the past on this Appalachian rail line.

One day a year it is legal to jump off of this astoundingly tall bridge that spans an Appalachian gorge.

A small storefront museum explores the history and myth of West Virginia's famous urban legend.

A particularly creepy abandoned hospital that sparks interest for lovers of the supernatural.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

Enormous lake at the bottom of a unique cave system.