An architect's childhood fantasy treehouse made real.

Native Americans built this circle of stones, which was used to predict astronomical events.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

A beautiful geyser under environmental threat.

The first declared National Monument in the United States.

All that remains of this once-booming mining town are the ruins of a saloon.

The site of the gruesome massacre—and maybe cannibalism—of five men, a tragedy that made Alferd Packer infamous.

This nearly abandoned town was once a thriving mining community until a series of fires.

This National Natural Landmark is one of the best examples of a “mass wasting” in the world.

An enthusiastically interactive mining museum that won't let black lung ruin the fun.

The site of a defunct mill, that once supplied marble for the construction of the Lincoln Memorial.

Air Force Academy Chapel made of 100 identical tetrahedrons works to inspire those of all religions.

At one time this small mining village was the highest town in America but now it sits abandoned while the mine churns on.

The final resting place of American icon Buffalo Bill, and a museum that aids in telling his tale.

The largest source of fossilized insects anywhere.

The Denver airport is guarded by a 32-foot-tall sculpture of a demonic horse.

The highest paved road in North America winds its way up Mount Blue Sky in Colorado to an altitude of 14,130 feet above sea level.

This Colorado hiking trail provides a small gold mine of abandoned gold mines.

The highest bridge in America was built for an almost unnervingly small amount of money.

When ecosystems collide in the arid Southwest.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.