Gneiss Creek: This is one of the best trails for spotting wildlife, especially early in the morning. Look for elk, eagles, moose and grizzly bears—check the safety section to learn how to stay protected in such areas. This is an 8.6-mile round trip hike and will take you from Montana into Wyoming. Don't forget to stop and fish at the Eponymous Creek.
Trailhead: Gneiss Creek Trailhead
More: 10 Southern California Hikes With Waterfalls
Hard
Sportsman Lake: This hike takes 3 to 4 days to complete, 23.6 miles total, and provides one of the best wilderness experiences you can have in the park. Remember to purchase a backcountry permit, and prepare to traverse rivers, creeks, majestic peaks, and pristine lakes—all in a remote and uncrowded paradise. Note: Don't attempt this hike if you have minimal hiking or remote-backpacking experience.
Trailhead: Glen Creek Trailhead.
Sky Rim: The high-altitude photographic scenery makes this one of the most notable Yellowstone hikes on the list, but is reserved for the experienced and physically fit; the route is an 18-mile lollipop loop. Keep your head up to catch unbelievable mountain vistas and views of wildlife. Check the weather before hiking this trail, as there's a lot of exposure on the ridgeline.
Trailhead: Dailey Creek Trailhead
View of the Lower Falls at The Grand Canyon of Yellowstone
More: What do Do at Rocky Mountain National Park
Find a Campground at ReserveAmerica.com.