From the outside, Newgrange looks like a giant grass-topped hill, ringed with huge white quartz stones that sparkle in the sunlight. Inside, a narrow stone passage runs into the middle, where there is a small chamber with a high stone roof.
The most amazing thing about Newgrange happens once a year. On the shortest day of winter — the 21st of December — the rising sun shines through a small opening above the door. The light travels down the long passage and fills the inner chamber for just 17 minutes.
Whoever designed Newgrange 5,000 years ago understood the sun's path so precisely that they could line up the building to catch it on the exact right morning. There were no maths books, no computers, no telescopes. They worked it out by watching the sky.
Today, thousands of people enter a yearly lottery to be inside Newgrange on the winter solstice. Only a small number get to stand in the chamber when the light beam arrives. The rest of the year, visitors walk into the passage and a special light is used to show them what it looks like.