Traquair House
Scottish Borders, United Kingdom
Traquair House, approximately 7 miles southeast of Peebles, is claimed to be the oldest continually inhabited house in Scotland. Whilst not strictly a castle, it is built in the style of a fortified mansion. It pre-dates the Scottish Baronial style of architecture, and may have been one of the influences on this style. The estate contains the famous Traquair Brewery.
Country house data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).