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

This maze-like slot canyon is a unique gem within an already fascinating geological area.

Rare recess caves fill this unbelievably beautiful Ohio park.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

A meditative space out of a fantasy story.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

Ruins of the elaborate house where the enigmatic costume designer threw glamorous parties for New York's theatrical elite.

An abandoned castle owned and ignored by Masons carries a cursed history.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

An abandoned stretch of highway, deteriorating next to the operational one.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

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

Oregon's unexpected high desert, displaying layers of time in a colorful show.

Quite simply the largest tree in the world (by volume).

The largest earthwork effigy in the world.

Tour the sci-fi-esque reality of governmental disease management.

Each year these high desert hills are absolutely covered with poppy flowers in a surreal show of nature.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

The world's longest known cave system.