Visited 25th September 2002: The Buwch a'r Llo and Mynydd March stones are very easy to find, but I've only just found their neighbour, a small stone called Castell Coch.
Castell Coch means red castle in Welsh, and it seems to be named after the nearby farm (I have no idea how the farm came to get it's name). Coming from the direction of Penrhyn Coch it's beyond the cattle grid on the right-hand side of the road, hidden in amongst the reeds. Although it's near the road, I only spotted it by chance. I'll not spoil your fun by giving you the grid reference!