To be privately owned
Friedrichshafen Castle

Originally a Benedictine monastery, Friedrichshafen Castle stands on the shores of Lake Constance in the city of the same name.
History+
Around 1085, Berta, wife of Count Otto I of Buchhorn, founded Hofen Monastery as a Benedictine nunnery. The nearby parish church of St. Andreas and Pantaleon was subordinated to the monastery. Around 1100, the Welfs handed it over to their house monastery, Weingarten Abbey, which subsequently sent a provost to manage it. In the 13th century, the monastery received its name after the neighboring hamlet. After an attempt at self-governance, the monastery was dissolved in 1419 at the behest of the Abbot of Weingarten, and its assets were managed as a provostry. In 1524, Überlingen sold the monastery to the city of Buchhorn, which in turn sold it to Weingarten Abbey in 1548. During the Thirty Years' War, Swedish troops burned down the monastery buildings in 1634.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Friedrichshafen_castle.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: 47.6497, 9.4652