Castle Island, Scotland
Castle Island () or Allimturrail is a small tidal island, lying off the east coast of Little Cumbrae, and to the west of Trail Island, in the Firth of Clyde. It is joined to Little Cumbrae at low tide. The castle which gives the island its name was built in 1527, and was destroyed by Cromwellian forces in 1650. It is a square keep, and is said to have been built originally to prevent deer poaching. Footnotes

Islands of the Clyde
The Cumbraes
Islands of North Ayrshire