Visited 15th December 2003: I spotted this stone as we drove along the road between the National trust car park and Carreg y Big. It's on the eastern side of the road, not far from one of the rocky outcrops that sit between the road and the lake. I was immediately struck by the obvious packing stones around the base of the stone, especially those on the eastern side. I wonder whether anyone has recorded this site before.
As far as I can see this stone is not listed anywhere, so it may not be prehistoric. Having said that it certainly looks the part, but it's so extremely obvious from the road that I can't believe it might have been overlooked by the archaeologists.
I've named the stone Ffridd y Beudail after the nearby farm house. I'm afraid the grid reference is not very accurate, because I didn't have my GPS with me when I visited.