Newgrange, Drogheda

This part of the Boyne Valley has many prehistoric monuments, the most important being the 'passage graves' of Newgrange, Knowth and Dowth. These huge stone and earth mounds are approximately 5,000 years old....predating the Pyramids of Egypt and England's Stonehenge.
Newgrange is the best known of the three. The entrance stone features some neolithic carvings and at sun rise on the winter solstice a shaft light illuminates the tomb through a special opening in the roof, quite an amazing piece of calculation by our prehistoric ancestors.
All visitors to the complex are filtered through the Bru na Boinne Visitors Centre, quite interesting in itself, explaining the history of the site and the archaeological techniques used to learn about it. The complex gets very busy, especially in summer, so it's highly recommended to arrive as early as possible. Not only to beat the queues but also the strict quota on visitor numbers into the tomb itself.
Further info available at the website