Drive into lot 3, the first big parking lot at Mt. Sunapee, then go to the right end of the parking lot and drive up the dirt road through an old gate. Follow this horrendously bumpy road until you hit another gate by the campground, and park there. Then walk down past the gate and up the the bottom of the sun bowl chairlift, turn left here and walk up the dirt road that goes uphill left of the lift; this is Williamson. Hike up this road until you see the boulder, it's directly off the road. You can't miss it.