Newgrange, a prehistoric site, is a must see when going to Ireland. It is older than Stonehenge and the Pyramids in Egypt. It is only about an hour or so from Dublin in the Brú na Bóinne complex in the River Boyne area. No one knows exactly what it was built for, although there are some theories. The coolest thing is that on winter solstice, the light from outside comes into a hole cut above the door and lights up the inside chamber. When you tour the site, they replicate this and it is really amazing. There are also some pretty cool carvings in the stone. If you are going to Ireland, put it on your list. I've been there twice and it was no less amazing the 2nd time around!