To be privately owned
Heyden Castle

The Heyden Castle Ruin is located in Horbach, a northwestern district of Aachen. Historians consider it to have been the complex of its kind in the Aachen region during the Middle Ages.
History+
Knight Arnold von dem Bongart, whose father Gottfried von dem Bongart resided at Haus Bongart, had Heyden Castle built at the beginning of the 14th century. As early as January 21, 1304, he made it available to the Count of Jülich as an open house. The castle served as the seat of the feudal lords who, in 1361, gave the area north of Aachen, around Richterich and Horbach, the name “Heydener Ländchen.” The Bongart family received the sub-lordship for life in 1370. From 1375, the complex was owned by the von Gronsfeld family before passing to the von Merode-Rimburg family in 1406, who held it until 1452. Subsequently, Haus Heyden came to the von Schönrade family, who acquired hereditary ownership in 1500. From 1547, the von dem Bongart family was again the owner, sometimes jointly with the von Leerode and Hochsteden families, and remained so until the 20th century.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=845
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: 50.8446, 6.0579