The Castle Trendelburg lies west of the Reinhardswaldes in the Hofgeismarer Rötsenke, which stretches between Vellmar in the south and Bad Karlshafen in the north.
The Spornburg, located at 172 m above NHN, is situated on a steep slope to the Diemel (river) sloping mountain ridge of sandstone on three sides. To the west, the terrain is only slightly down. The medieval town of Trendelburg, with its Gothic church and historic Town Hall, is located to the castle walls. Parts of the city walls are preserved or reconstructed.