To be privately owned
Wernstein Castle

Wernstein Castle, a historic castle complex, stands on a granite rock directly on the Inn River in the municipality of Wernstein am Inn in Upper Austria. It is known for its construction as a curtain wall castle, where the buildings are integrated directly into the castle wall.
History+
The first documentary mention of Wernstein Castle dates back to the 12th century. Around 1126, it was built by the Counts of Formbach as an outpost of the Neuburg Castle located on the opposite bank. Wernstein was never the seat of an independent noble family, but was always administered by the castellans of Neuburg. In 1200, an Ortlof de propugnaculo, also known as Ortlof ob der wer, is mentioned. After the Formbachs, the castle, together with Neuburg, passed to the Counts of Andechs-Merania. Through the marriage of an Agnes from this family, it came into the possession of the last Babenberg duke, Frederick II, but had to be returned to the Andechs family after his divorce. Premysl Ottokar II forcibly occupied Neuburg and Wernstein in 1257. Around 1355, Eberhard von Wallsee redeemed the Passau pledge on the castles. Duke Albrecht III pledged Neuburg and Wernstein to Otto von Zelking in 1379. Emperor Maximilian I sold the County of Neuburg to Nikolaus Graf Salm in 1518.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:070415_Burg_Wernstein.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: 48.5050, 13.4543