This is the best riding on Cape Cod period. The best stuff is through the woods, its mostly single trail with some fast little down hill sections and excellent little climbs that just flows together. Its got some pretty technical sections. As far as length, i spent the summer riding out there and i didn't cover all the possible trail combinations. Also there is a chance you could get turned around and somewhat lost but its all part of the fun(unless its getting dark of course). Anyways anyone up in that part of the woods its definitely worth checking out. Oh by the way there is a gun range next to the trails don't be alarmed, after all i'm here to write about it . Oh also this trail is LEGAL to ride on!!!!!
If you are on Route 6 get off on Exit 5(aka 149). If comming from the east turn left and go about 50yards then turn right onto Service Rd. Go for about 100-150yards there will be a little entrance on the left. You can park there. If comming from the west or from the direction of boston get off on Exit 5, then take a right or head south on Rte 149. The Service Road is the first right after you get off the highway. Then follow the rest of the directions from above.
http://www.singletracks.com/item.php?c=1&i=260