Old Castle Lachlan

Castle Lachlan, or Old Castle Lachlan, is a ruined 15th-century castle on Loch Fyne, Scotland. It was the stronghold of Clan MacLachlan until 1746 when it was attacked by British Government forces. New Castle Lachlan was built as a replacement in 1790, around 1 km to the north-east.

It is protected as a category A listed building, and as a scheduled monument.