Take a hard right just before the Chapel at the end of the road to Selmun. It's a one-lane track about 2km down ot the beach. The are to park in is another 200m along an even smaller track and you'll have to do a 3-point turn to get around the corner in to the road.
Make sure you don't block it up for other users - park carefully as the terrain is clay and just a little rain will see you stuck.
