If you like outdoor activities, I can recommend taking a hike up Mount Hooiberg (early to beat the heat). Not too strenuous. I think a average person can make it up the paved walk and 562 steps. Once on top (ignoring the cell towers and exposed wiring) the views are worth it!

If you will have a car, a ride along the coast where the arches are is worth a few hours. The rugged coast and dry landscape is worth a look. I believe that there is a donkey sanctuary in that vicinity.