There's a very active area called Lower Geyser Basin. This shot shows a small bubbling pool in the foreground and the mountains to the West. The view in person is so spectacular this picture pales in comparison.
There were also a few thermal areas that had things called paint pots. Instead of heated water, they had what looked like warm clay or mud. They made a fabulous gurgling noise as they bubbled and churned.
Here's another hot pool that bubbled away with a great view in the distance.