The drive down into the canyon and along the river is worth doing. Drive slow and careful as the roads are very twisty and there can be a lot of debris (rocks, etc) on the road. But the views are fantastic and the granite canyon is impressive. The river at the bottom is worth checking out. There's also a cave that does public tours- Boyden Cavern. Spend some time in the slow safe parts of the river (close to roads end) and also do the Roaring Falls walk (it's short, less than 5 minutes). The waterfull is beautiful (but do stay out of the water, people die there from falling in!). The river in the summer isn't too cold to enjoy, my kids had fun swimming for over an hour.