Craters of the Moon National Monument and Preserve

North Crater Trail Idaho's lava fields look unfinished, as if the eruptions stopped last week, and the pick for walkers is the North Crater Trail: 3.5 miles round trip with 758 feet of climbing, along the rim of North Crater, down into the mouth of the vent that fed the North Crater flow, past the rim of Big Craters and on to the Spatter Cones. It shows more kinds of volcanic feature in one outing than almost any trail on this list. The footing is cinders and lava rock that the park itself calls rough and jagged, so wear proper shoes. Off-trail walking is not allowed at the Spatter Cones, which protects fragile formations that are easy to break.