I came across this on a previous trip back down from Seahan Hill and was curious. The camera battery was dying a rapid death and the light was fading fast so I split and said I'd return. I approached it from one of the forest tracks on the left of the Ballinascorney to Kilbride rifle range road. It's the one with the largest entrance and has a forestry barrier. Walk along this track for about a mile (you will start to descend after about 300 yards – don't worry, keep going). At the end of the track there is another steep track on your right hand side (due east). Head up here and make sure you check out the quartz encrusted boulder at the top. You'll meet another track crossing here. Turn right and walk for another 100 metres or so and bam, there it is, just inside the tree-line.
How can I describe this? Best thing is to look at the shots. However, if you're up here, check out the views to the east and north, just over the fence and 100 metres into the heather. The day I was there, low cloud hung over the city to the north and all the way up Glenasmole valley. Beautiful.
Another 123 metres higher, and about a mile further south up the track you were on, is Seahan Hill, which you'll want to visit.