You definitely need the OS maps, no's 84 and 79 I think, will check that. It's along a windy little road and is not visible until you are right beside it, sitting on a platform above the road. It must be only 80ft or so from the road but unless you know it's there... Views are jaw dropping though, as well as being a beautiful little circle so it's worth the effort. I'll have a look at the maps again, directions are possible but there's so many little entrances and tracks it's hard to tell which turn off is which after you leave the little village on the main road.

If you're in the area there, you could take the wild mountain road down towards Bantry and visit these: http://www.themodernantiquarian.com/site/2595/maughanasilly.html
http://www.themodernantiquarian.com/site/2561/ardrah.html
http://www.themodernantiquarian.com/site/7425/gortnacowly.html
among many other fine sites mentioned already.

Uragh West is something on a similar vein on the Beara Peninsula, bit of a scramble but the isolation and ancientness are worth it:
http://www.themodernantiquarian.com/post/55443/images/uragh_west.html