To be privately owned
Lismore Castle

In County Waterford, Ireland, stands Lismore Castle, a structure of historical significance, currently in private ownership.
History+
The origins of the castle date back to 1185, when Prince John had a castellum built on this site. After ascending to the throne as King of England, he transferred the estate to the church, whereupon it served as a bishop's residence until 1589. Subsequently, the castle came into the possession of Sir Walter Raleigh. In 1602, during his imprisonment for treason, Raleigh sold the estate to Richard Boyle, later the 1st Earl of Cork. Lismore was also the birthplace of Robert Boyle, Richard Boyle's youngest son, who was born here in 1626 and became known as a philosopher and the father of modern chemistry.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 52.1406, -7.9337