This standing stone isnt marked on the OS map. It is on the top of Luddenmore / Buchillbreaga.
It is about 2.25m in height. From below it looks huge altogether.
There is also the strange broken ruin of some kind of turret. I dont know what it was for. Perhaps it had something to do with the antennas that are up here but i doubt it because it is held together using lime mortar.