Twentymile Lava Trail is a 9.6 mile moderately trafficked out and back trail located near Idaho Falls, Idaho that features beautiful wild flowers and is rated as moderate. The trail is primarily used for hiking, walking, and trail running and is best used from March until October. Dogs are also able to use this trail.

A 0.9-mile loop or a 4.5-mile trail to the main vent of the flow. Both are unimproved and marked with poles. Hiking in lava fields is unique because of the rough terrain, unusual scenery, and the contorted landscape. Since this is a Wilderness Study Area (WSA), permanent trails have not been developed. The unimproved hiking routes are marked with poles. Blue top poles mark a route around a short loop which is a good introduction to lava hiking. The 0.9-mile loop takes about 30 minutes to walk. On this loop note the pressure ridges, deep cracks with ferns at the bottom, and moss on rocks. Red top poles mark a 4.5-mile route to the main vent or source of Hell’s Half Acre lava flow. This is a strenuous hike and a round-trip to the vent can take a full day. Water is essential and boots with good soles are advisable. Estimated time to hike to the vent is 2-3.5 hours (one way).