Of course, Yellowstone is more than just volcanic activity. It has also amazing wildlife (buffalos, foxes, coyotes, deer, bears, bald eagles). I saw all except foxes and grizzlies. Foxes are shy and I missed seeing the grizzlies.
Also, there are wonderful canyons and water falls.
Here are some images of the scenery:
and a few panoramas:
Of course, I took photos of the wildlife:
Finally, 2 panorama photos of Grand Teton National Park which I also visited, which is stunning:
Enjoy.