GPS: 46°16'N 122°54'W
Ape Cave formed in a hurry when a channel of lava pouring from Mount St. Helens cooled and crusted over at the sides and top even as the molten flow inside continued. The result is a lava tube roughly 2.5 miles (4 kilometers) long, one of the more unique hikes in the Northwest or anywhere else. Choose the longer Upper Ape Cave if you have basic rock climbing or caving experience. Piles of large, sharp boulders block the way, and you must surmount Lava Falls, an eight-foot (two-meter) wall with less than obvious holds. Otherwise, opt for Lower Ape Cave. Same eerie darkness, same glistening moisture on black basalt, only shorter and easier.
Originally published in the April 2008 edition of National Geographic Adventure