The eroded core of an ancient volcano is now accessible by a short hike.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

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

A nature and cultural preserve named for its multitude of petroglyphs carved by the Northern Sinagua people.

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