To be privately owned
Alnwick Castle

In Alnwick, Northumberland, Alnwick Castle stands as England's second-largest aristocratic residence after Windsor Castle. It has served for centuries as the ancestral seat of the Percy family, whose heads hold the title of Duke of Northumberland.
History+
The origins of Alnwick Castle date back to 1096, when Yves de Vescy erected the complex to secure England's northern borders against Scottish incursions. It was first documented at the end of the 11th century. In the early 14th century, under Henry de Percy, the 1st Baron Percy, substantial parts such as the Abbot's Tower and the Constable's Tower were built, whose structures remain preserved to this day. Initial reconstruction and restoration work took place in the mid-16th century.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Alnwick_Castle_02.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: 55.4157, -1.7060