We have visited Yellowstone a least a couple of times that I can remember. The last time we were with our kids and it turned out not to be an enjoyable experience. We drove around and around and never did find a parking place and then left in disgust. This trip we happened to see signs for Yellowstone on the way back and decided, what the heck, we were not looking to stay so why not drive through with our Senior Pass and see what we could see. We made no attempt to see Old Faithful, but we saw plenty of interesting things.
We saw plenty of buffalo. I was quite excited when I spotted the first one off in the distance, but eventually we saw many more close to our car. Too close to play naive tourist and get out for a closer look.
We spotted plenty of instances of the geothermal activity. Geysers in the distance, but powerful steam vents up close. I remembered the bubbling mud pots from my first visit and I kept searching for something similar to what I remembered. I was able to find a few tame versions.