Yes Newgrange is over there, it was a fascinating site but the day we went there were hordes of people and you had to book a place with a guide and it would have been a long wait so we just looked at it from a distance
However, there are lesser know megalithic sites very close to Newgrange that get less attention - and some of these were amazing; with wonderful rock art of spirals and mazes.
Ireland definitely has a lot to offer for the megalithic site enthusiasts!. Though Scotland isn't too far behind and we have lots up here too.