I wanted to in Yellowstone a while back but the park ranger said you could get some fucked up diseases from them. Whether or not that's true, who knows?
sun valley has some nice ones up warmsprings a couple miles. its prettty much in the an eddie that people have damed up a little. gotta catch it when the water is low or it will be nippy
Went to the ones in pagosa they were built up but still sick since they were basically empty and get to some natural ones I think it was in la fortura Costa Rica springs were amazing since they were all natural just in a river