Once you climbed up the Heiligenberg mountain you can understand why already during the Iron Age humans used this place to build a fortification. It is a nearly 400 meters high basaltic mountain and the first castle was built here between 1180 and 1186 CE. Today you can visit the remaining walls, a well-preserved gate, you can use one of the many places to sit down for a picnic or climb up onto the short tower to enjoy good views on the city Felsberg.
A private association cares about the castle ruin and voluntary workers keep it in good shape. Underneath the castle, you can find a restaurant and hotel (the ‘Burghotel‘) and parking lots. From there it is only a short walk up the hill. If you take the longer walk up from Gensungen you can discover some artworks in the forest on an Ars Natura hiking path. Within the gate to the castle grounds, you can see a bell: it has been placed there in 1952 as a memorial for those Germans that lost their homes in the former East of Germany and settled in the region (nearly 10,000).