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

A Saint Nicholas-themed ghost town in the Mojave desert.

Abandoned silver mine strewn with wrecked and twisted structures.

The largest self-built castle in the U.S., six decades in the making.

The largest source of fossilized insects anywhere.

Air Force Academy Chapel made of 100 identical tetrahedrons works to inspire those of all religions.

This grand stone tower was dedicated to a famed American humorist almost by coincidence.

The moving metal works of one troubled artist can still be viewed on his front lawn... for now.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.

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

Dramatic river bend surrounds a natural red-rocked pedestal.

Legends surround this jagged rock formation in the New Mexico desert.

These once-beautiful historic graveyards are set against the barren Virginia City hills.

Beneath a Virginia City bar is the entrance to an abandoned gold mine.

These huge stone ovens in the desert fueled the Nevada silver boom, and may have also been a hideout for outlaws.

This cave was hidden for thousands of years, storing the worldly goods of ancient Native Americans.

A roaring, awe-inspiring double cascade of icy water flows through woodland Oregon like something out of a Tolkien novel.

This large maar crater in Oregon is the bigger brother to Hole in the Ground.

On the Oregon coast there is a natural hole that seems to be draining the sea.

A Roman-style column in Oregon hides a spiral staircase inside.

The longest continuous lava tube in Oregon.

Massive crater in central Oregon.

World's largest porcine hairball sits in a collection maintained by Benedictine monks.

Bridges, terraces, and replicas of historic structures all built of rock and petrified wood by one man.