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

These Pre-Columbian petroglyphs contain representations of birds, deer, hunters, and even some early Native flute players.

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

A phenomenal assembly of pueblos in New Mexico is the most complete example of ancient ruins north of the border.

Legends surround this jagged rock formation in the New Mexico desert.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

Site of the 1879 Cheyenne Outbreak and the site where famed Sioux chief Crazy Horse met his fate.

America's largest man-made forest was planted in an effort to bring back the past.

Otherworldly rock formations and ancient fossils abound in this unique stretch of Nebraska badlands.

This erect, phallic geological spire wasn't always named so domestically.

An experimental, automotive replica of Stonehenge.

During the summer, surfers in Alaska take advantage of this inlet’s unusual water patterns.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

This WWII-era military installation once held an entire city within its walls - now, its walls are falling down.

A trading post in the North Pole where children send letters.

The king of U.S. high points towers over every other peak on the continent.

Mind-blowing carvings and fantasy ice scenes grace the largest year-round ice environment in the world.

A skeletal collection of former nautical mainstays.

Launchpad for the US military’s dead mouse operation to battle millions of snakes.

Located on Guam's south shore, this small cave is named for an ancient and powerful Chamorro Chief.

The ruins of a once-grand mansion in Northern Ireland are now thought to be haunted.

The ruins of this medieval castle in Northern Ireland have inspired artists from C.S. Lewis to Led Zeppelin.

Northern Ireland's Brobdingnagian stepping stones.

The library houses an incredible collection of some of the world's most impressive books and manuscripts.