"Newgrange ... is a prehistoric monument in County Meath in Ireland, located on a rise overlooking the River Boyne [5 miles] west of Drogheda. It is an exceptionally grand passage tomb built during the Neolithic Period, around 3200 BC, making it older than Stonehenge and the Egyptian pyramids. It is aligned on the winter solstice sunrise. Newgrange is the main monument in the Brú na Bóinne complex, a World Heritage Site that also includes the passage tombs of Knowth and Dowth, as well as other henges, burial mounds and standing stones." (Wikipedia)
The Stone Age art found at Newgrange and these other mounds is really spectacular. According to Wikipedia, "Newgrange contains various examples of graphic Neolithic rock art carved onto its stone surfaces.These carvings fit into ten categories, five of which are curvilinear (circles, spirals, arcs, serpentiniforms, and dot-in-circles) and the other five of which are rectilinear (chevrons, lozenges, radials, parallel lines, and offsets)."
Video from 2011. Closed captions useful.