An artificial crater field that trained astronauts for lunar exploration.

Thousands of Mexican Free-Tailed Bats soar around an abandoned storm drain at sunset each summer.

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

Witnessing the might of this dessert-colored desert waterfall is a rare, powerful treat.

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

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

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

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

One of the word's deepest gorges is also tied to a fantastic legend.

The stunningly blue waters of these beautiful caves also have a violent past.

On the edge of the Valles Caldera National Preserve, these rock formations create an eerie landscape.

This stunning waterfall is the backdrop to a site that has seen continuous human habitation for 250,000 years.

A centuries-old lookout post still sits atop a natural stone spire.

This ancient Hindu temple is covered in thousands of colorful statues and has a long mythological history.

A former bastion of Rajput chivalry, this massive hill fort is the site of legend and tragedy.

An extraordinary "City of Caves" carved from solid stone.

This abandoned fort is said to be the most haunted place in India, so much so that entry is prohibited after sunset.

This magnificent stepwell is designed as an inverted temple and adorned with 1,500 sculptures.

A complex of six forts embedded in the Rajasthan hills.

A single tree's 2,800 aerial roots give the appearance of a complete forest.

Rock-cut cave complex filled with ancient Buddhist artwork.

The second-longest continuous wall on the planet protects a hidden secret in the deserts of India.

This complex of vertically-excavated Buddhist, Jain, and Hindu monolithic temples in India's Maharashtra providence illustrates a spirit of tolerance characteristic of ancient India.

Centuries-old bridges grown from tangled roots.