We downloaded the app the night before entering Yellowstone National Park via Cody, Wy. Our intention was to take the circle of fire tour offered by the park, but the app provided great detailed commentary and gave us flexibility to move at our own pace without worrying about missing key points of interest. The app worked perfectly throughout YNP regardless whether we had cell service or not. We saved $200 in tour fees and missed nothing. Neither did we waste time wandering about aimlessly not knowing where to stop or turn. I wish they had an app for the black hills of SD as well.