We used to live near the Montana entrance of Yellowstone. I always preferred going to the park in fall. The crowds are much smaller then and trying to drive through the park in summer can be maddening. In fall you also have a better chance of having some attractions to yourself, or at least not having to stand behind rows of people. Also, the Elk are in rut in the fall and you will see large herds of them together and hear bull elk bugling. As for things to do, there are so many, Yellowstone is very large. Old faithful of course, Yellowstone falls, Glory pond. There are also many attractions that you can hike to. Here is a site with some great info on Yellowstone and Yellowstone activities www.greatwildlifevacations.com Hope this helps you.