We stayed at West Yellowstone and drove into the park each day. With Golden Age passport, there is no admission charge. Plan at least 5-7 days, especially if you expect to do more than just drive through. for Example, Paint Pots is at least a good 4 hours to see fully and enjoy, time plus the hike to get there. Sign in parking lot says Paint Pots 3/4 mile. That is to the end of the walkway. Most of the other places are the same. Plan on taking some time, and enjoy the park. Old Faithful is a must see, at least 2 hours to see eruption, plus time to get there, find parking, walk around and see the sights. Plan in time to hike some trails if you are able. Of course, we tend to walk slower, and spend a lot of time looking at things. We don't know how much time we actually have left to see things, so we try to see as much as we can while we can.