It's always interesting visiting old homes. Wander around Kasteel de Haar and try to visualize how this historic residence once functioned.
You'll have sightseeing choices galore when in Loosdrecht. Kasteel de Haar is a great place to start here, but there are many other worthwhile places to visit. Loosdrecht Lakes, Vinkeveense Plassen, and Hilversumsche Golf Club are near the historically significant residence and will round out your day nicely.