The remains of the castle can be visited
CastleBad Pyrmont - Oesberg
Hünenburg Castle

The Hünenburg is the ruin of a hilltop castle on the Königsberg near the Oesberg district of the city of Bad Pyrmont in the Hameln-Pyrmont district in Lower Saxony. The Hünenburg is the oldest ruin in the region.
In 1910, remains of the walls of a residential tower surrounded by ramparts and moats were uncovered. Excavations of shards, knives, horseshoes, nails, and sickles suggest that the castle complex, which extended to the west, was founded between the 9th and 10th centuries. The castle presumably perished in a fire around 1100.
Image: Rabanus Flavus / CC0 via Wikimedia Commons
Location: 51.9879, 9.2699