Classic hiking area in Yellowstone
Slough Creek drains from the northern part of Yellowstone National Park and the Absarokas into the famous Lamar Valley. While Lamar attracts daily crowds of cars looking for wildlife, Slough is only accessible by foot and horse (and one concessionaire's wagon).
It's classic Yellowstone country -- not so many spectacular mountains but beautiful high country with lots of wildlife. You can hike dozens of miles into reaches of the Gallatin National Forest far from any road. Supposedly the fly fishing is also wonderful but I haven't tried that.
Access begins at the Slough Creek Trailhead, a few miles off the Northeast Entrance Road. (There's also a developed campground there.) There are eight backcountry campsites along Slough Creek between the trailhead and the park boundary; after that, Gallatin NF rules on dispersed camping apply.
These pictures are just a taste of the area. Feel free to attach yours.