Achanduin Castle, (also known as Achadun Castle and Acha-Dun), is a castle, now in ruins, located about 5 kilometres west of Achnacroish on the north-western coastline of the Isle of Lismore, in Argyll and Bute, Scotland. The castle overlooks Loch Linnhe and Bernera Island. The ruins are thought to date back to the thirteenth century. Achanduin Castle had long been thought to have been built by the Bishop of Argyll, though recent research has proved this to be unlikely. The castle was likely built by the MacDougalls around 1290 who held it throughout the fourteenth century.