Don't forget to bring your camera to capture the flowing cascades of Coo Waterfall. If it's raging, you may be able to feel the mist on your face.
You're spoiled for sightseeing choice when in Grand Coo. Coo Waterfall is a great place to kick off here, but there are numerous other interesting places to appreciate. Circuit de Spa-Francorchamps, and Abbaye de Stavelot are not far from the cascade of water and and will cap off your day nicely.