The remains of the castle can be visited
Sachsenstein Castle

The castle ruin Sachsenstein, an imposing defensive structure in the Harz foreland, bears witness to the turbulent history of the 11th century. Its remains, perched on a mountain spur, offer insights into the military architecture of the Salian period and are now a freely accessible testament to past power struggles.
History+
The construction of Sachsenstein Castle was initiated by the later Salian Emperor Henry IV to secure his rule in the Harz foreland. It is among the eight castles mentioned by Lampert of Hersfeld as early as 1073. The complex was characterized by an unusual construction, including a large round tower and a gate chamber flanked by two hexagonal towers – an arrangement unique in the 11th century. The masonry technique used, with layered stonework and a herringbone pattern in the core, is typical for Salian castles from the mid-11th century onwards. It is believed that the castle was never fully completed. The ministerials stationed at such fortifications collected taxes from the local population, which led to the uprising of the Saxons against Henry IV. In the Peace of Gerstungen in 1074, the king was forced to commit to the demolition of the castles.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Roland Neubert, Halle (Saale)
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: 51.5877, 10.5813