Should be called Fairy Castle, I think. 

Google Maps has this down as 'Fairy Castle'. Also, my copy of Joss Lynam's 'Easy walks near Dublin' (which I trust) has this location as Fairy Castle, and 'Two rock' as the location 500m along the path to the S-E (marked 'Two rock' on this map). The first image here https://en.wikipedia.org/wiki/Two_Rock shows the 2 rocks which I'm guessing are the ones to the S-E. 

Sorry I lack the skills (and confidence) to make the change. 