West Thumb
The West Thumb hot spring area is right on Yellowstone Lake, only a couple miles from the camp gound at Grant's Village where we stayed. It's a fairly active site, and part of Yelowstone Lake is the West Thumb Caldera. Incidentally, Yellowstone Lake is huge.
To give you an idea of the size of the lake, I've marked that narrow neck of the lake where the Caldera connects to the rest of the lake. I also marked it on the pic below. That's what it looks like from the shoreline at West Thumb, which is basically opposite that narrowing on the caldera rim. You can take boats on the lake, but you're not going to want to ski. The wind whips up at a moments notice, and the water is cold. Typical is in the 40's.
This is one of the views from the boardwalk.
Some of the vents are physically in the lake itself.
These three pics are of our favorite hot spring at West Thumb, the Abyss Pool. It's 53 feet deep.