Have you ever been to Yellowstone or Grand Teton National Park, and if so, can you share your experience here?

I’m tossing around summer vacation ideas, and am pondering the idea of driving to Yellowstone and/or Grand Teton National Park. I know there’s a lot of information on TripAdvisor and Facebook about it, with hotel reviews, day trips, and lots of talk about where the good scenery is, how much time to spend, etc.

Have you ever been to Yellowstone or Grand Teton? If so, can you tell me about your experience? Do you have any advice or tips to share?