The remains of the Castle can be visited
Greenan Castle

A 16th-century castle ruin, Greenan Castle, is situated on the coast of Ayr in South Ayrshire, Scotland. The structure was likely built on the foundations of an older fortification.
History+
The lands of Greenan were forfeited in 1476 by John, Earl of Ross and Lord of the Isles, due to treason against King James III. In 1493, James IV granted the lands to William Douglas, son of Archibald, Earl of Angus. In 1603, the castle belonged to John Kennedy of Baltersan and his third wife Florence MacDowell, whose initials and the year can be found above the entrance. In May 1602, Sir Thomas Kennedy of Culzean, who had spent the previous night with his half-brother John Kennedy of Baltersan, was ambushed and murdered on his way to Edinburgh.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Colin Jackson
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: 55.4386, -4.6702