In reply to goldmember:
Couple of Anglesey ideas:
park at Benllech, coast path south then east to back of beach at east end of Pentraeth Forest, making sure the tide is low (vital to check that out!!) head North west across Red Wharf Bay on the sand (with the odd channel to cross) all the way back. Can extend run into Pentraeth Forest if wanted.
Newborough Forest: park at Pen-lon (NE corner of forest). South down coast path, then west on beach, across and around island (unless tide is high), north along beach, find way back to coast path and cut across the north of the forest back to car (need map for this bit)