Little Cumbrae Castle sits on Allimturrail or Castle Island, a small tidal island, situated off the east coast of Little Cumbrae, in the Firth of Clyde. It is designated as a scheduled monument.
Wikipedia https://en.wikipedia.org/wiki/Little_Cumbrae_Castle
Address KA23 9, United Kingdom
Coordinates 55°43'12.555" N -4°56'34.378" E