When ecosystems collide in the arid Southwest.

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

The clock that sets them all.

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

The remnants of the base where US Army troops learned how to fight in extreme conditions.

At the tallest peak in Colorado, an electrifying mix of thin air, lightning, and rivalry.

The largest source of fossilized insects anywhere.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

There's more contention than one might expect from cherry pie pans.

Watch the ships come in on Michigan's 210 ft. high observation deck in Sault Ste. Marie.

This lighthouse and shipwreck museum keep a torch burning for the memory of the SS Edmund Fitzgerald.

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

This shallow cave got its name from copious amount of human bones found inside.

Island where motor vehicles are banned -- home to the only carless highway in the United States.