There are two buildings known as Castle Lachlan here: New Castle Lachlan is an 18th century baronial house; Old Castle Lachlan, described here, is a 15th century stronghold on the site of older fortresses going back to at least the early 1300s.
The Maclachlans fought with Bonnie Prince Charlie during the Jacobite uprising, but the clan chief died at Culloden and the castle was abandoned then. There is a tradition that the castle was attacked by an English warship from Loch Fyne.