Peter Duniho wrote:

As long as you're in the vicinity, Lassen Volcanic National Park in
California's good too. Sort of a smaller, more accessible Yellowstone.

There is also the volcanic area just south of Bend. You can hike into a mile
long lava tube and back out. Cool and dry. Bring your own lantern(s)
flashlights or rent a lantern from the park. I recommend long pants and a
fleece jacket when down in the tube.