Take the boat shuttle across Jenny Lake to the Cascade Canyon trailhead. Just a different way to start a hike.
If you don't mind stairs, hike down to one of the viewpoints in Yellowstone Canyon to see the falls from a better perspective.
Of course a hike around the Lower Geyser Basin is a must. Stop in at the Old Faithful VC and check out the anticipated eruption times to see if you can plan a loop to see some of the other geysers erupt (besides Old Faithful).
Walk out onto Fishing Bridge and look down at all the large rainbow trout swimming below you.
