the rock is to the west of the main area
you have to go over a fence and past a "keep out" sign ( don't remember exact words, basically a NPS liability release, "If you get hurt it's not our fault because you were where you shouldn't have been" )
I think you could also get there by going to the left and low on the slope rather than following the paved trail all the way out to the point.
There's another vista point with railings down there. There used to be ( may still be ) a bunch of antennas pointed down into the valley attached to the railing. There's some coaxial cables coming down from the radio shack on the side of Sentinel Dome. TV stations used to be relayed down so that there was reception in the valley. All the TV antennas in the valley would be pointed at Glacier Point!
One of the best views of the rock is from the upper part of 4-mile trail. The upper part of the trail is on the west slope of the Ledge Trail gully and as it goes north you get some great views of the rock with HD in the background