This naturally-sourced hot spring is now home to a clothing-optional resort.

This unique structure in suburban Austin is made up entirely of other people's castaways, and constantly changing.

A self-built castle made by a mysterious man.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

A breathtaking array of ancient Pueblo structures and artifacts counterintuitively preserved by neglect.

A trash dump made beautiful by nature's power.

The first declared National Monument in the United States.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

Mysterious rocks that ring musically when struck.

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

Here, at the "world's longest art gallery," you'll find forty miles of ancient petroglyphs and pictographs.

Stroll through a wonderland of stupendous moss-covered trees.

Enormous lake at the bottom of a unique cave system.

America's most famous piece of self-built architecture.

One man's homage to the sun continues to grow like a glass fractal.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

Giant busts of 42 U.S. presidents are sitting in a field in Virginia.

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

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

Under the right circumstances, this waterfall in Yosemite briefly turns a luminescent fiery orange.

The land is full of geologic eye candy, such as otherworldly spires, mushroom-shaped hoodoos, and prehistoric fossils.