Rick:

Great picture of Yellowstone Falls.

At Yellowstone, there's a great hot springs suitable for soaking, between the North Entrance and Park HQ. It's called the Boiling River. It isn't signed, presumably because the Park Service doesn't want to encourage too much use. You park in a large parking lot, and it's about a 1/2 mile hike, give or take, on a streamside trail to the hot springs. I've found the site pretty well populated, but usually not too crowded. The hot water comes out of a fissure on the bank of the river, too hot for soaking. Where it mixes in the main stream, there are places where the water temperature is just right.

I never worked Yellowstone National Park during my lengthy National Park Service career. However, once while vacationing, I happened upon a medical emergency on the side of the road near Old Faithful, and assisted. After the victim was loaded into an abulance, a Park Ranger who I worked with at another Park recognized me and asked what I was doing there. "Just helping out", I replied.