The six-mile-wide caldera in the heart of Aniakchak National Monument and Preserve showcases what's left when a mountain literally blows its top.

But that's not all you'll find in this 600,000-acre park perched in Southwest Alaska near the start of the Aleutian Chain. The area is also well known for the wild Aniakchak River, which alternates peaceful stretches with challenging whitewater; and easy but trail-less walking across the caldera floor. But Aniakchak's greatest offering may be solitude, with only 150 visitors in a typical year.