The remains of the Castle can be visited
Altendorf Castle

The Altendorf Castle Ruin in Essen, a hilltop water castle, is on a peninsula south of the Ruhr river. It houses the largest preserved residential tower between the Rhine and Weser.
History+
The origins of Altendorf Castle date back to the second half of the 12th century, when it was built in the Romanesque style. The complex underwent alterations and expansions, adding Gothic and Renaissance elements. Owners included the noble families of Vietinghoff-Schell and von Mumm. In the mid-19th century, the castle passed into bourgeois private ownership.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=575
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: 51.4171, 7.1239