In the middle of a suburban Denver neighborhood is a cave that once provided solace for a prominent Ute chief and his family.

Intensely colorful calcite pools in Southern China.

A 140-year-old castle with underground caves hidden in San Francisco.

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

Dramatic river bend surrounds a natural red-rocked pedestal.

Wondrous sandstone hoodoos where Native Americans collected clay for pottery, 9,000 years ago.

An emerald-green grotto just a short trip from Austin.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

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

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

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

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

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

An improbable waterfall springs from an orange-white cliff face, tumbling into the headwaters of the Virgin River above Zion National Park.

A small oasis not far from downtown Moab.

An Ancestral Puebloan ruin that appears to burst into flames in the sunlight.

Few things look more out of place than the electric blue ponds in the reddish-brown desert of Utah.

A tunnel with windows, so you don't miss out on the impressive views.

This quiet park's strange sedimentary spires were named after Kodak's color film.

The fifth-longest natural arch in the world, and the longest outside China.

Despite its name, this route in southern Utah offers a heavenly day trip.

Once a menacing challenge for trailblazers, this trail is now the most scenic drive in Utah.