Several open access pools of perfect hot water on public land in the wild west of Caliornia near the Nevada state line, hard to reach so usually few people. Some weeks in spring the river water is high enough for rafting groups coming in on weekends. Otherwise it's a two hour hike or, in winter, a back country ski tour. In late summer the river level is low enough for 4x4 jeep enthusiasts (also unfortunately often gun and booze toting) to get there.