The remains of the Castle can be visited
Asseburg Castle
On a narrow ridge of the Asse mountain range not far from Wolfenbüttel is the Asseburg castle ruin, a former hilltop castle. It was known as the largest hilltop castle in Northern Germany and considered impregnable.
History+
The Asseburg was constructed between 1218 and 1223 under the direction of Gunzelin von Wolfenbüttel. Originally conceived as a joint inheritance castle, it was one of the largest medieval complexes in Northern Germany, with a length of approximately 180 meters and a width of around 50 meters. Its defenses included five successive courtyards, secured by gates and transverse walls, as well as three towers and a cistern. Despite initial resistance, as the construction took place on Welf territory and on land belonging to Gandersheim Abbey, Gunzelin prevailed.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: https://commons.wikimedia.org/wiki/File:1-asseburg-wittmar.JPG?uselang=de
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 52.1395, 10.6353