When you speak of something that is 5000 years old it is beyond my comprehension, yet that is the age of Newgrange, a 5000 year old tomb in Ireland.  Just think of it, it was built one thousand years before Stonehenge, three thousand years BC.  How did they physically do that?  How did they know to align it so  perfectly to capture those first rays of the dawn's sun on the winter solstice?  So many questions and so interesting!