Summer Lake hot springs: The springs are located in the "Oregon Outback" on a remote plot of land near Summer Lake. It's a small collection of scattered buildings and campground off OR-31. There is a large salt flat neighboring the campground, with snowcapped mountains in the distance. The actual hot mineral springs are housed in a large house/barn (pictured above) but they also have outside hot springs in the back of the building. There are horses grazing on the property and the people are laid back and kind. It feels like a true Oregon retreat. Really soothing, and very beautiful.
Umpqua hot springs: Located in the Umpqua National Forest, these hot springs are in the middle of the forest, surrounded by pines and overlooking the Umpqua River. You can park at the trail head, then hike about a half mile up hill to the hot springs. There are several "pools" you can soak in, and when I went there were only a few other people. Being in the middle of the forest makes it feel very private and wild. I hadn't seen anything like it before, it was truly stunning.
Highly, highly recommend checking them both out.