I have looked at these five red dots on the OS map for years now with the intention of visiting them. Finally I made the effort to drive across Dublin and up the coast to make this trip: it's actually more of a pain to drive 15km across Dublin than it is to drive to Sligo!
The GPS reading given here is for the main mound. The GPS readings for all five lounds are O 19663 66002, O 19691 65998, O 19728 65997, O 19780 65979 & O 19821 65910.
This is an amazing location. Sitting on the largest mound and watching the sea crash in below you, totally immersed in the sound of the waves breaking against the rocky shore is a beautiful experience.
500m to the north is the spot where the Delvin River enters the sea. Beyond that is the passage tomb cemetery of Knocknagin (County Meath), the two acting as sentinels to the narrow route inland towards Fourknocks (County Meath) and then Tara beyond that.
To the southeast the twin rocks of Rockabill lie breastlike on the horizon. Further south Lambay Island can be seen again on the horizon.
Of the five mounds the central on is the largest at over 3m tall and 30m across. The other four appear to be satellite tombs to this one. There may have been more to the north of the main mound at one time, but these would have been washed into the sea so we'll never know.
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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.