A hotbed of geothermal activity, Lassen Volcanic National Park has mud pots, boiling pools and fumaroles (an opening near a volcano which releases gas).

There’s boating, kayaking, and fishing in the park, but hiking through a lava tube at Lassen is one of the park’s singular experiences. Try the wincingly-named Bumpass Hell Trail – so named for Kendall Bumpass who fell into scalding water here – for views of boiling mudpots, turquoise pools and Brokeoff Volcano. Alternatively, try the 4.2 mile Devil’s Kitchen Trail for steaming streams and alpine lakes.

Lassen is one of the best places in California to go star-gazing. Park rangers lead astronomy tours during the summer, and the annual Dark Sky Festival, held in August, offers nightly stargazing tours and talks by professional astronomers.