The imposing, wooded rock massif "Alte Burg" is located southwest of the town of Rodalben above the Eisenbahnstraße, is geographically based on the Grünbühl and protrudes into the valley in a northerly direction. Its field name "Entenstein" is defined by geologists and historians as "anti-stone" (directed against the attackers), partly derived from "Enzenstein" (huge stone). This rock massif is popularly known as the "Old Castle" and is also recorded under this name in the topographical hiking maps of the Palatinate. The hiker will look in vain for a ruin or castle there, because according to a report by the historical researcher Dr. Daniel Häberle from 1910, the old castle is a prehistoric refugee castle, to which the Celtic indigenous population of the entire valley could retreat with all their cattle and portable belongings in the event of raids. To the east, north and west the rock walls are very high and were almost invincible for the conditions at the time, so that the castle was easy to defend. An effective attack was only to be feared towards the south, where the rock faces stop on both sides and where the mountain cone is connected to the Grünbühl by a mountain saddle. According to Dr. Häberle, "put art in a state of defense". He continues: "So the north and east, as well as the south of the mountain height, were well secured. And the west? Here is a very wide incision in the rock over a length of about 100 paces up to the rocks rising on the north side The inclined plane of the mountain cone was made, thereby creating for the defenders about 20 feet wide, level and manageable terrain. Here the enemy could easily be deterred on the very steep, western side of the mountain, even pieces of rock that were deliberately thrown down the mountain."
Today, hikers can get an impression of the mighty rock faces if they follow the Rodalber Felsenwanderweg, on which the "Old Castle" is located - between the Fohnbach and Hettersbach valleys. As a beautiful vantage point, it is very popular for a Vesper. In the evening the rock massif with its exposed location is illuminated.