It would take 35 firetrucks to fill this enormous glacial pothole.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

This hidden gem of a garden has one of the only surviving Victorian ferneries in America.

When the Austin Dam failed it destroyed much of Austin...and then it failed again.

This California artist's front yard acts as a gallery for his unique, scrap metal animal sculptures.

Home of a 28-foot tall stalagmite known as the War Club.

These rows of World War II-era bunkers were the scene of some of the infamous Mothman sightings.

This large cave is a summer home to thousands of bats and has a rich history dating back to prehistoric times.

Live long and prosper in Tennessee.

Wild lights and sound effects turn a walk through some caves into an eye-popping 1960s tourist attraction.

Better known as the "Body Farm," this unique research facility has been studying how human bodies break down since the 1980s.

The mysterious wonder of an underground waterfall is illuminated by multicolored lights.

The secret city built by the Manhattan Project.

Enormous lake at the bottom of a unique cave system.

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

All that's left of the quintessential "cabin in the woods."

A 12,000-year-old bog boasting rare plants and fauna.

This 1,700-pound edible sculpture is way better than your average chocolate mousse.

This tiny patch of arid sand sits in one of the greenest states in the United States.

A morbid secret lies hidden within the beautiful walls of the Boston Athenaeum.

A cabinet of curious mathematical models and old calculators.

This old selenite mine is dotted with tiny crystals that make it shimmer like it's covered in glitter.

The eroded core of an ancient volcano is now accessible by a short hike.

The highest point in Arizona is an oddly snow-topped peak within the otherwise arid state.