The remains of the Castle can be visited
Apenburg Castle

The Apenburg castle ruin, also known as Groß Apenburg or Alte Burg, is a lowland castle in the Altmarkkreis Salzwedel in Saxony-Anhalt. Situated amidst a marshy landscape on an artificially created hill.
History+
The origins of the first castle complex, Apenborch Castle, date back to the year 1000. This was located approximately 100 meters west of the current site and belonged to the noble family of Apenborch. In 1343, it was destroyed along with the associated settlement. The current Apenburg Castle was built in the 13th century, concurrently with the development of the town, and served to secure the Purnitz Pass.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Apenburg_Bergfried.jpg
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: 52.7071, 11.2050