When we were in Ireland we visited Newgrange, a neolithic tomb that is 5000 years old, which makes it older than the pyramids at Giza and 1000 years older than Stonehenge. This mega tomb was built completely without metal tools and is really, really huge. In fact we saw other passage tombs that had not been completely cleared away and they resembled hills. What is remarkable is that the passage way to the burial chamber in the depths of the burial mound is perfectly aligned with the rising sun on the winter solstice. As the sun rises over the horizon, the light creeps along the roof of the passage way and just as the sun clears the horizon it illuminates the burial chamber for a brief moment before creeping back down the floor of the passage as the sun climbs higher in the sky. What is remarkable is that our ancestors 5000 years ago were able to figure out precisely the angle and inclination of the passageway to achieve this and were able to build it into their tomb without our modern technology. In fact they didn't even have metal tools but were using stone, bones and wood to build this. This is truly awesome and is a testament to human ingenuity.
Newgrange Neolithic Tomb
The passageway in Knowth the sister tomb to Newgrange
The entrance to the tomb, the opening above the entrance permits the light to enter on the winter solstice. Notice the spirals carved on one of the entrance stones, these spirals are found carved on many of the stones used to built the tombs and probably had great spiritual significance.