Lassen Volcanic National Park

Bumpass Hell Trail This is where you see a volcano breathing. The park says its hottest and most vigorous hydrothermal features are at Bumpass Hell, and a three-mile round-trip trail, first built by the Civilian Conservation Corps in 1935, leads to a boardwalk that threads the basin's boiling pools and hissing vents to a turnaround just north of Pyrite Pool. Stay on the boards: the ground here is thin and scalding, and shifting features have already forced part of the old walkway to be removed. Timing matters too. Heavy snow can keep the trail buried well into summer, so this is a late-season walk in most years.