Keoneheʻeheʻe (Sliding Sands) Trail
Walk down into the crater, then climb every foot back.
Keoneheʻeheʻe drops off the rim near Haleakala's summit and reaches the crater floor in 3.9 miles, about 2,500 feet down through cinder and silence. Every foot comes back up in thin air, so budget double for the return. The park's own tip is to leave the car at Halemauʻu and hitch to the trailhead so you finish where you parked.