1. Aniakchak National Monument and Preserve, Alaska

Number of visitors in 2018: 100

Aniakchak may be best-known for its consistent status as the country’s least-visited national park site, seeing fewer than 300 tourists in a typical year. It’s not only remote — accessible by a long journey of flying, boating and/or backpacking — it’s also a rugged, difficult environment, with foggy, rainy weather and a high concentration of bears and wolves. For those brave few who do venture down the Alaska Peninsula and into the monument, the area’s other best-known feature awaits — a jaw-dropping 6-mile-wide, 2,000-foot-deep volcanic caldera. Within this deep, ashy crater is Surprise Lake, source of the Aniakchak River, as well as Vent Mountain, a 2,200-foot-tall cone formed by a volcanic eruption in 1931. For more on the hardships and thrills of traveling to Aniakchak, read Christopher Solomon’s gripping 2014 travelogue in Outside magazine.