Just on an interesting side note about Newgrange, which i find massively impressive and am shocked you missed it, is: there is a hole in the forementioned feature above the main door that, on the 21 of December every year- the winter solstice, or shortest day of the year-, the sun shines directly through when it rises, flooding the entire tunnel and tomb with light in every recess of it giving it an almost unearthly glow. I have never seen it myself as, unfortunately, the waiting list to visit on that day requires several years of booking ahead. It is a shame, i live here and i still can't see this wonderful work of ancient architecture/astronomy in action.