This place has alluded me for quite a while. Its been on my 'todo' list from the moment I saw it in a old OS map (and realised that it wasn't all fictional).
I have spent quite a while in the past searching for this place, both using satellite images, walking around the area and research on the internet - the main problem is that the area that it is in private land which is working game land, the other being that there are in fact three 'known' graves within a very short distance. This grave is the one where he was buried, there is another one in a very stately homes residence and the other is in a grave yard in a church near to this site.
My sincere thanks to Nick for his assistance in getting to this place (he visited it about 15 years ago)
The story goes that Robin was wounded and went to get refuge and medical assistance from the nunnery (which still exists, but is on private property and is a no go area - a big shame), the nuns poisoned him (how or why is unclear) and on his deathbed, he fired a arrow and stated where ever it landed he was to be buried.