Limestone caves with spectacular showcase chambers.

An artificial crater field that trained astronauts for lunar exploration.

Ancient pueblos built into the base of a natural canyon wall.

This Arizona observatory is famous for investigations into Martian life, and as the place humans first spotted Pluto.

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

After a short-lived attempt to bring America in line with the rest of the world, this road was left in metric.

America's only nuclear missile silo open to the public.

A spiritual vortex among the red rocks in Sedona.

On the outskirts of a reborn ghost town, a decaying post office remembers the bad old days.

A Wild West jailhouse that slid down the mountainside.

A reproduction of earth's many biomes.

The largest natural travertine bridge in the world is nestled in a small canyon in central Arizona.

An urban laboratory.

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

This collection of Wild West movie memorabilia also claims to hold some secrets of the Lost Dutchman's mine.

A geological mystery on Camelback Mountain.

A self-built castle made by a mysterious man.

Every Christmas, one Arizona city makes the most of its dry climate by creating an arid desert tannenbaum.

Honoring the famed folktale author, this California museum looks like it belongs in the Black Forest.

An alley covered with 20 years of bubble gum.