Although I came very close to visiting this site, we parked on the wrong side of the road and missed the offical car-park and the Tumulus completely. See fieldnotes for the Pierre du Sacrifice for the full story.
This site has been now been included on the TMA Google Earth so check it out before visiting and you won't make the same mistake as I did.
Page showing views of Tumulus de la Boixe, Pierre du Sacrifice and general information on the Boixe Forest from the French Wikipedia website. Note - page also contains location maps and detailed GPS coordinates for sites in the forest