This was on our very hot, final day in Yellowstone. We missed out on getting a campground there for a third night, so we altered our plans and decided to head east into Montana a day earlier... which paid off with the trip across Beartooth Pass. But before we got that far we made a point to stop at the Boiling River, a geothermal hot springs that flows from Mammoth and into the Gardiner River. The water from Boiling is over a hundred degrees (hence the appropriate name) while the water in the Gardiner is about 50 degrees, so you can sit in these pools and have your feet in cold water and the rest of you in very, very hot water. It is a pretty cool experience. The perfect way to while away those hot days.