A self-built castle made by a mysterious man.

An urban laboratory.

The largest natural travertine bridge in the world is nestled in a small canyon in central Arizona.

A partial tunnel blasted into a steep ridge is all that remains of a failed railway across Arizona.

A unique collection of artistic rides

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

A spiritual vortex among the red rocks in Sedona.

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

The artist James Turrell is repurposing an extinct volcano crater as an observatory to experience the cosmos.

Dramatic river bend surrounds a natural red-rocked pedestal.

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

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

This Native American settlement dates back to the Pueblo II period.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

One of the most extensive and well-preserved collections of dinosaur footprints in North America.

Most-visited and most-photographed slot canyon in the American Southwest.

A riverside tiny house with books and other treasures galore.

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

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

This ancient cave is home to a museum, bar, and is filled with fluorescent minerals.

This raised bulls-eye visible from space was the subject of an intense geologic controversy.

The eerie ruins of an isolated abandoned town nicknamed "the Widowmaker" for its deadly gold mine.

Narrow slot canyons in a badland eroded into soft sedimentary rock provide an otherworldly landscape in this remote Nevada state park.

Settled by the Church of Jesus Christ of Latter-day Saints in 1859, this abandoned frontier town has appeared in several films.