To be privately owned
Grillmayr Castle

In the Kleinmünchen district of Linz, Upper Austria, Austria, stands the Grillmayr Schlößl, a former factory owner's villa. It is distinguished by its early historicist architecture and its history as a summer residence for prominent entrepreneurial families.
History+
The history of the Grillmayr Schlößl began on April 7, 1845, when Johann and Katharina Grillmayer acquired the Steinbruckmühle, which had existed since at least 1419. This purchase included not only the buildings but also important water rights on the Weidlingerbach, which were crucial for the family's planned spinning mill.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Linz-Kleinm%C3%BCnchen_-_Grillmayr_Schl%C3%B6%C3%9Fl_01.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: 48.2525, 14.3213