While the former may have existed one day, we visited the latter in South Dakota, between Devil’s Tower and Grand Teton.

A view of the travertine terrace from the hanging bridge over the river

Hot Spring State Park surrounds the largest hot spring in the world, pumping out millions of gallons of 127 deg F water every day. After walking around the spring, its pools, and its terraces of travertine, we took a much-needed and relaxing soak in the free hot spring-fed pool. (Fortunately, the water is cooled to 104 deg before entering the tub!)
Just what the doctor ordered for my stiff back after many hours between a car and an air mattress!