To be privately owned
Prugg Castle

Prugg Castle is a building in Bruck an der Leitha, Lower Austria, that served as a border fortification and later as a palace. Originally built as a castle to protect against Hungarian incursions, it was reshaped and expanded multiple times.
History+
The origins of Prugg Castle date back to the 11th century, when the area was a donation from King Henry IV to the Bishop of Freising. The first documented mention of the former moated castle occurred in 1242. Due to its strategic location on a bridge over the Leitha, which once formed the Roman imperial border, the border castle held military importance in the Middle Ages. It withstood numerous attacks but had to be surrendered in 1484 after a six-week siege by the Hungarians and again in 1529 during the First Turkish Siege. In 1560, the castle was pledged to Baron Leonhard IV von Harrach and fully passed into the possession of the Harrach family during the Thirty Years' War.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Schloss_prugg_bruck_an_der_leitha_frontside.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: 48.0258, 16.7827