The passage grave at Newgrange was built 5,200 years ago even before the pyramids.
It was aligned so that a chamber deep underground lights up with sunlight just as the dawn sun brakes the horizon on the morning of December 21st.
It was a remarkable achievement for those who built it using horse cart and hand given it required thousands of tonnes of rock and earth.
Each year hundreds of people flock to Newgrange to be there on the solstice morning, with a lucky few chosen by a lottery winning the right to be in the chamber at sunrise.
The chamber only lights up because of the very fine alignment of the access passage to the rising winter solstice sun. The light actually enters via a shoebox-sized gap above the passage entrance.