If you're looking for outdoor fun, make sure you visit The Wetterhorn. No walk around the block, this hike is great for some mid-vacation exercise.
You'll have no end of sightseeing choices when staying in Grindelwald. The Wetterhorn is a good place to begin here, but there are lots of other worthy sights to explore. Jungfraujoch, Eiger, and Kleine Scheidegg are near the steep landmass and will fill in your day nicely.