This cromlech is actually rectangular, and forms the starting point of the Kerlescan stone rows. Fenced off from the multitudes access is only by small guided tours. I intended to come back later in the evening for a wee sneak but never gone the chance. So I only saw it from the road, fleetingly, between tourists and stables.
Fortunately Sir Aubrey (why not) describes it thoroughly, abbreviated thus...........
Tall granite pillars in a rectangle 78m x 74m, on the right side, from the road, the east side of the rectangle is a straight line of 18 stones, the south side nearest the road is a shallow convex arc of 11 stones, the left west side is equally convex and also of 11 stones. There are no stones at the north side, but close to it is a neolithic long mound called a tertre with a tall menhir at it's western egde. The three sided structure is therefore more of a horseshoe.
I wish I'd had time to come back later, it sounds a very curious site.