Between the Sauer and Gaybach rivers, the Castellberg plateau rises above the valley and the village of Wallendorf. As early as the 4th century BC, a Celtic settlement was established on the more than 40-hectare site. Around 130 BC, the Celtic Treveri then built a large city-like settlement, an oppidum, which was protected by a mighty surrounding fortification wall. Before the Gallic War of Gaius Iulius Caesar (58-50 BC), it was one of the most important settlements of the Treveri. Treverian coins, including silver and gold coins, were minted here.

After the conquest of Gaul by the Romans, a temple district was built on the highest point of the mountain around the birth of Christ. A small settlement of traders and craftsmen and perhaps pilgrims' quarters adjoined the local sanctuary. The settlement was partially abandoned in the course of the Germanic invasions in the 3rd century and then completely abandoned at the end of the 4th century.

From the so-called "Römerturm", a wooden observation tower on the edge of the plateau, you have a wide view over the valleys of the Sauer and Our rivers and into neighboring Luxembourg.

The Castellberg can be reached with a short detour, for example via the circular hiking trail 44 of the Southern Eifel Nature Park .