An abandoned saucer-shaped monument in the Bulgarian mountains.

UNESCO-protected ancient burial ground.

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

Ruins of an early Roman Christian church dating back to the 4th to 5th centuries.

This historic black and white monastery is one of Bulgaria's architectural jewels.

Underneath this Byzantinian church lies a necropolis filled with ancient tombs and the ruins of previous churches.

Bizarrely shaped rock formations in northwest Bulgaria come with equally bizarre legends.

A striking symbol of the Bulgarian capital.

One of the largest mines in Bulgaria is now home to a vast museum more than 100 feet underground.

The remains of Abó, Gran Quivera, and Qurai are monuments to the long, complicated history of the Indigenous people of the Southwest.

Explore a misty river canyon from a metal bridge system.

The oldest continuously occupied public building in the United States.

The hallowed remains of a 900-year old Ancestral Pueblo great house.

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

Thousands of pieces of art have been carved into the rock at the site of an ancient volcanic eruption.

One man’s passion for gas stations is on display along the Rio Grande in northern New Mexico.

Home of the International Space Hall of Fame.

This volcano rises like a giant anthill from the plains below, with a road spiraling up to the rim.

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

The official atomic museum of the United States explores the explosive and productive history of a much maligned energy source.

A cave's rare beauty held a cavernous secret hidden underground.

Despite time, colonization, and the brutal New Mexican heat, these Pueblo ruins still stand.

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