Newgrange is a passage tomb built around 3100 BC on a rise above the River Boyne. The mound is about 85 metres across and 12 metres high, ringed by carved kerbstones, and its front is faced with white quartz. A 19-metre passage leads to a cross-shaped chamber with a high corbelled roof that has kept out the rain for five thousand years. On the winter solstice the rising sun shines through a "roof box" above the entrance and lights the chamber floor for about 17 minutes.
You can only visit on a guided tour from the Brú na Bóinne Visitor Centre, and tickets go fast in summer. The tour ends inside the chamber, where the guide recreates the solstice light with lamps. The passage is low and narrow, and photography inside is not allowed. The quartz front is a 1970s reconstruction by the archaeologist Michael O'Kelly and is still argued about; look closely at the huge entrance stone with its triple spiral, which is the real thing.