Yellowstone National Park is visually spectacular! The stunning colors of the geysers, hot springs, and paint pots in the southwest quadrant of the park along the Firehole River are a landscape photographer's dream. Other impressive landscapes within the park include the Grand Canyon of the Yellowstone, the Hayden and Lamar Valleys, Lake Yellowstone, and Mammoth Hot Springs. My recommended guide is "Yellowstone Treasures" by Janet Chapple (even the park rangers use it as a reference).