An arsenic-filled pool in the Grand Canyon takes on the appearance of a giant, overflowing pumpkin.

A self-built castle made by a mysterious man.

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

The installation’s official name, “You Who Are Getting Obliterated in the Dancing Swarm of Fireflies,” says it all.

Some of the tallest ancient American ruins continue to inspire awe and curiosity.

What is the Thing?

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

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

The wreckage of a deadly bomber plane crash can still be found near an Arizona peak.

One woman's UFO-themed campground, complete with self-built energy vortexes, UFO-themed weddings, and magic bushes.

A stealthy Apache hideaway that became the haunting site of a mass grave.

Ancestral Puebloan ruins, natural arches, and box canyons abound in this seldom-visited corner of Monument Valley Navajo Tribal Park.

Wee (and not so wee) footprints that insects and reptiles of the Paleozoic Era left behind.

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

Gleaming self-built castle towers made from beer cans and inspired by "Vitamin Mary Jane."

Crumbling remnants of what was once a booming town full of silver.

A museum dedicated to the alleged Roswell Incident.

These ruins of a pre-Columbian cliff village are among the most beautiful and well preserved in New Mexico.

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

Home of the International Space Hall of Fame.

The world's first commercial spaceport is a disappointment of cosmic proportions.

The ruins of this abandoned fort now stand as a picturesque reminder of America's march West.

A clear blue swimming hole with hidden caves, still unexplored.

A phenomenal assembly of pueblos in New Mexico is the most complete example of ancient ruins north of the border.