Newgrange was Druids chief place of worship
Druids were in the land of Ireland thousands of years before the arrival of the Celts and they did build Newgrange. They also built Stonehenge and founded the ancient Egyptian priesthood, of which Moses was an initiate.
Later, a corruption of Druidry, called Christianity, came back to Ireland, and through bribery of the Irish kings and their forces , wrought total destruction on the Order of Druids.
