Aniakchak National Monument & Preserve

Aniakchak is one of the least-visited places in the National Park System: a volcano on the Alaska Peninsula that has erupted at least 40 times in 10,000 years, until a 7,000-foot mountain collapsed into a caldera 3,300 feet deep. Surprise Lake fills part of the crater floor, and the Aniakchak River escapes through a gap called the Gates.

There are no roads, trails, or facilities; visitors arrive by air taxi in famously difficult weather to see the caldera. For a challenge, expert adventurers can join a guided fly-in expedition to raft out through the Gates, one of the wildest undertakings in the park system.