To be privately owned
Attenbach Castle

On the left bank of the Sieg in Hennef is Haus Attenbach, a noble residence that lent its name to the district. This two-story structure, featuring its two round corner towers, represents the type of a lowland castle.
History+
The exact founding date of the castle complex is not known. The place name Attenbach was first mentioned in a document in 1142 in the property registers of Nonnenwerth Monastery, with other sources citing an earlier mention in the abbey's foundation charter from 1126. In 1367, it is documented that the then owner, Knight Johann von Attenbach, derived his name from the castle. At the beginning of the 16th century, the estate passed to Arnold von Vünfzahl. His heiress, Maria, married Wilhelm von Gevertzhagen and brought the castle into the marriage.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.zeche.org/
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: 50.7696, 7.3472