This may or may not be a genuine standing stone. It is certainly not marked on the OS maps. What struck me about it is that it is in a direct line between Fairy Castle on the top of Two Rocks Mountain and Howth.
From the R113 in south Dublin follow the signs for the Wicklow Way and park in the car park at O150 245. Follow the Wicklow Way until you are nearly at the top of Two Rocks around the west side. You will see a path leading east towards the television mast on Three Rocks Mountain. Head for these and you will come to a very stoney path up to the cairn. The stone is about half way up this track 50m or so to the right.
This is an explanation of (and a bit of a disclaimer for) the coordinates I provide.
Where a GPS figure is given this is the master for all other coordinates. According to my Garmin these are quite accurate.
Where there is no GPS figure the 6 figure grid reference is master for the others. This may not be very accurate as it could have come from the OS maps and could have been read by eye. Consequently, all other cordinates are going to have inaccuracies.
The calculation of Longitude and Latitude uses an algorithm that is not 100% accurate. The long/lat figures are used as a basis for calculating the UTM & ITM coordinates. Consequently, UTM & ITM coordinates are slightly out.
UTM is a global coordinate system - Universal Transverse Mercator - that is at the core of the GPS system.
ITM is the new coordinate system - Irish Transverse Mercator - that is more accurate and more GPS friendly than the Irish Grid Reference system. This will be used on the next generation of Irish OS maps.