Very technical and fun. Some freeride stuff. Some's sketchy. Stay to the west of powerlines and loop back to the parking lot. Good view of Atlantic Ocean if you don't mind the huge ugly power plant down below.
Take rt 3 north from Cape Cod or south from Boston. Take exit 3 to 3A. Take left. Park at dirt road on the right of 3A before bike shop and drop in singletrack at South end of lot.
http://www.singletracks.com/item.php?c=1&i=1588