My understanding is that 'Craigh na dun' does not exist. Merely it was an idea created from Clava Cairns, an ancient burial ground dating back to 3000AD situated to the rear of Culloden. Diana Gabaldon took inspriration from the standing stones that surround the ancient 'cairn's' at Clava and based the fictional 'Craigh na dun' from this.
Something is not right. This message is just to keep things from messing up down the road