So what if you want to visit Yellowstone National Park over two days, what can you do? For those of you unprepared or not a bus tour here are some recommendations. The main thing is, unlike any park I’ve ever visited, this thing is truly massive. I had always thought Jackson Hole was right next to Yellowstone. I didn’t realize it was hours and one national park (Grand Tetons) away. It takes three days to see it all and this is with a car.
Still it is insanely crowded in the summer and there are ten big “hits” according to Yellowstone.net although you could spend a lifetime visiting, here are the top ten in priority order 
1. Old Faithful Geyser and Upper Geyser Basin. Hey this is the most famous spot and pretty concentrated since it is only a small one square mile. There are five predicted geysers, but see the GRand if you only see one. You start with a visit to the Old Faithful Visitor Center. So if kids are impatient, go on to the Lower Basin and take the short Fountain Paint Pots Trail which has more stuff going on.
2. Grand Canyon of the Yellowstone. The falls are 100 meters high and a great photo. Look at it from both sides and tkae the 3/8 mile hike to the edge of the Lower Falls. Amazing views.
3. Hayden Valley. This is in the center and is wildlife central. There are lots of turnouts, so you can do this by car. You should see bison, elk and maybe even a bear!
4. Mammoth Hot Springs. This is park headquarters and has a nice visiter’s center. Take the Terrace drive for sure.
5. Yellowstone Lake. The largest high altitude lake, visit the Lake Village for sure.
6. Norris Geyser Basin. YAG (Yet another geyser) make sure to see Echinus and also take the boardwalks.
7. Lamar Valley. Another wildlife heaven, it is no. 7 because it is far away in the remote northeast. But get there if you have time.
8. Tower Fall. The second most popular falls. Hike to overlook and also down to the base
9. Lower Geyser Basin / Fountain Paint Pots. It is #1 if you are less patient because Fountain Paint Pots is so accessible. Otherwise the rest is much more spread out
10. West Thumb Geyser Basin. Nice because it is near Yellowstone Lake and in fact some of the thermals are in the lake itself.