June 30, 2006—It's the final resting place of countless Stone Age dead, but mystery still lives at Ireland's Newgrange tomb.

Scientists have long been puzzled by the massive 5,000-year-old mound, but one revelation shed a lot of light—literally—on the meaning of the crypt. On the winter solstice, the shortest day of the year, a beam of sunlight reveals a corridor that leads to a cache of ancient bones.

Tour the halls of Newgrange, and explore the deep mysteries of one of Europe's most puzzling Stone Age sites.