Definitely approach this one from above. From the barrow head down the hill towards the Ballybetagh road and to you left. Seeing this come into view is great. The walls remain to a height of about 1m and within it you can see the rings and lines of stones that mark out rooms and buildings inside. It is about 60m in diameter with an entrance to the south. From its position on the slope of the hill it can only have been built to watch over the road below, whih leads to one of the passes through the Dublin Mountains.
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.