Yellowstone National Park is enormous! It's hard to appreciate how big it is until you actually try to see it. We had read that you need a good three days to see the whole park, and after being there, I would definitely agree. The park loop is 142 miles and is a figure 8. Driving is often slow due to other tourists, animals on the road, and animal watching. Also, you end up doing a lot of backtracking because you have to make it back to where you are staying each evening. In our almost three full days we were able to see nearly everything we had hoped. There was one hike we really wanted to do but the weather just wouldn't cooperate for the 7 mile hike. Oh well, next time.
We drove up from Grand Teton National Park and decided to try to do as much that first day as we could. The weather was supposed the beautiful that day and then get progressively colder and wetter over the next few days (which it did). We crammed a lot in that first day, but it was worth it. We got settled at our campsite and then tackled a bunch of sites. The geyser basins were incredible (I had seen them before, but they never really get old). We also saw the Grand Canyon of Yellowstone, saw a few smaller sites, and hiked Uncle Tom's Trail (and Bethany did the entire 500 ft/300 step descent and assent, much to the surprise of everyone we passed!)