Carn Wen is located in a big dark forestry plantation, a way through exists for those who are unfamiliar with stuff like suspension and exhausts, a road winds through the lost hillside, a maze of tracks that, judging by maps and google earth shift back and forth like the staircase at Hogwarts.
We drove carefully this way and that picking our way round the labyrinth carefully, but I'm afraid to say we couldnt find it, hidden as it was behind an impenatrable but protective wall of close fitting trees. Google earth, which has a good view of it, shows that if we had approached from the north an open avenue leads the way. But as if in concalation we found another cairn (of which I have posted a pic) really close to where we thought Carn Wen would be, so close that all the time I was there I was convincing myself that this was it.
Better luck next time I guess.