Dun Maraig

The tidal island of Dun Maraig in Poll na h-Ealaidh, Isle of Skye has the vague remains of a fort on it. Once it was connected to the shore by a causeway, and it is still possible to walk across to it at very low tide.
Perhaps more interestingly, the small island was won as the star prize in a 1994 German TV game show by a Stefan Schluznus of Bremen. A pretty useless, but fun, sort of prize.