Newgrange
How did a farming community without writing, metal tools, or (as far as the evidence shows) any recorded mathematics engineer a 19-meter passage to funnel winter-solstice sunrise into a chamber with such precision, and what did the tomb mean to the people who built and used it?
c. 3200-3100 BCE (Neolithic) · Brú na Bóinne, County Meath, Ireland