This sinkhole in the Arizona desert is filled with carbonated, arsenic-rich water

A planet-hunting astrograph built in the 1920s to seek out the so-called "Planet X" beyond Uranus.

This Arizona observatory is famous for investigations into Martian life, and as the place humans first spotted Pluto.

The final resting place of the businessman-turned-astronomer who helped discover Pluto stands near his observatory.

Ancient pueblos built into the base of a natural canyon wall.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

The tragedy of the Japanese internment camps is remembered here by a stark "Soul Consoling Tower."

Trails through lava-carved tube-caves display sparkling bacteria and a rich history.

This rugged area of red rocks and arches is often considered one of the most beautiful places on Earth.

This historic national park is covered in the stunning ruins of red rock pueblos.

Towering basalt columns, a creation of fire and ice.

This natural marble cave is one of only five national monuments in Oregon.

A small metropolis of Pueblo cave dwellings have been carved right into the hillside of this national monument.

Red sandstone structures dominate this landscape, which has been inhabited for some 5,000 years.

See massive fossils that are over 200 million years old in northeastern Arizona.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

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

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

A multi-storied adobe complex has been inhabited for more than a thousand years.

These aggressively sustainable art homes look like something out of 1970's science fiction.

A sprawling collection of over 106,000 toys from around the world.

The oldest continuously occupied public building in the United States.

This innocuous New Mexico storefront was once the secret jump-off spot for Manhattan Project scientists.

A small side chapel in Santa Fe's basilica is home to the oldest statute of the Virgin Mary in North America.