I visited Yellowstone in the winter once and hope to do so again. It's unbelievably beautiful then, and many of the animals hang around the geyser areas to find food and warmth, so they're easily viewed. We rented a snowmobile for a day and went to the Grand Canyon of the Yellowstone, also went cross country skiing and snowshoeing. I'm not sure I could still do all those things, but I'd like to try. Have fun.