The remains of the Castle can be visited
Calenberg Castle

The Calenberg Castle Ruin, a former medieval lowland castle, is located in Pattensen-Schulenburg in the Hanover Region, Lower Saxony. Originally designed as a moated castle and later expanded into a fortress, it gave its name to the Principality of Calenberg and played a role in Welf history.
History+
Duke Otto the Strict began constructing Calenberg Castle in 1292 in the Leine floodplains on a marlstone bank. In the early 16th century, it was converted into a fortress, which proved resilient and withstood several sieges, including during the Thirty Years' War. After this conflict, the fortress lost its military significance and was demolished.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Jörg Heldt
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: 52.1962, 9.7957