Haleakalā National Park

Keoneheʻeheʻe (Sliding Sands) Trail Walk straight down from the summit visitor center into a landscape of rust, black and ocher cinder cones. The "crater floor" is 3.9 miles down, an almost 2,500-foot descent, and the full crossing to the Halemauʻu trailhead is a classic 11-mile day past Pele's Paint Pot and the 65-foot Kawilinau pit. The catch is altitude: thin air makes every climb harder and altitude sickness is a real risk, and the park's rule of thumb is to allow twice as long coming up as going down. Going even a short way in rewards you, since a first overlook sits a quarter mile from the lot. There is no hiker shuttle, so through-hikers park at Halemauʻu and arrange a ride up.