The meaning behind this triumphal Roman arch was a mystery until the early 20th century.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

This unique structure is the only one of its kind in Virginia.

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

Atop this arch, during the 16th-century, a sermon was given to those suffering from plague.

The second-largest natural arch in the Chartreuse Mountains.

Many people don't realize there’s a lot going on in—and below—the world’s tallest triumphal arch.

The "Black Arch" guards the entrance to the picturesque Glens of Antrim.

A strenuous, unofficial trail leads to spectacular views in one of America's most remote national monuments.

A graceful natural rock formation stands astride the point where the Gulf of California meets the Pacific Ocean.

Tucked between a side street and a theater, this arch once led to a prestigious riding school, and now opens to a courtyard and community garden.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

Unlike most arches, this geological oddity formed in a volcanic dike.

This striking arch, one of the first architectural elements constructed in Prospect Park, was recently restored to its original glory.

This magnificent arch is all that remains of a former smelt mill.

It's safe—and permitted—to walk across these twin natural sandstone arches.

Once connected to the outside world by a single train track, this ghost town is looked after by the National Park Service.

This historic iron-working village is now a ghost town so immaculate that it looks as though it was recently built.

This eerily well-preserved coal town was saved from destruction by a Sean Connery movie.

A once-booming Mississippi River town with a history of racial violence is now eerie and mostly abandoned.

The ghostly remains of what was once the world's richest copper mine.

A living snapshot of a different time in America is preserved and maintained by a community of volunteers.

A ghost town originally established and governed solely by Black Americans seeking a place of their own, free from discrimination.

This deserted Gold Rush town is home to a Masonic lodge that, strangely enough, still holds meetings.