The only Florida state park with publicly accessible caves.

The so-called "world's shortest river" is actually a window into a cave.

Interactive modern and vintage submarine equipment, World War II relics, and submarine attire.

Ruins of a Carnegie family mansion on Cumberland Island.

This road in the Great Smoky Mountains was supposed to assuage a displaced community, but ended up a $52 million dead end.

North Carolina's finest examples of Native American pictographs have survived for 5,000 years.

Mile-long cave system near Great Smoky Mountains.

One of the Cemestos prefab homes built to secretly house thousands of Manhattan Project workers.

The secret city built by the Manhattan Project.

This intricate Hindu temple is the largest of its kind outside of India itself and was constructed like a giant puzzle.

Enormous lake at the bottom of a unique cave system.

Crumbling ruins mark the site of a couple's grisly murder in the woods.

One of the largest-ever mental hospitals now sits abandoned, surrounded by 25,000 unmarked graves.

An abandoned railroad tunnel forgotten by time awaits inquisitive hikers.

The remains of one of America's first radiation testing grounds still rest ominously in a Georgia forest.

The mysterious 855-foot zigzagging stone wall has been baffling people for centuries.