Newgrange is the best known of the Boyne Valley passage tombs. It consists of a large mound surrounded by ninety-seven kerbstones and covered by a massive cairn of water-rolled stones. Inside a long passage leads to a cruciform chamber that opens into three recesses. The roof is an architecturally outstanding corbelled vault with rows of masonry creating a cone-shaped roof. The roof-box directly above the entrance was built to allow the rays of the sun to shine directly into the chamber at the winter solstice. Three stone basins in each recess held the remains of the dead, most of which were cremated. Some of the art on the kerbstones and orthostats within the tomb are the finest examples of megalithic art to be found in Europe. The entrance stone at Newgrange is particularly well known for its striking sculpture while a fine example of the famous tri-spiral design associated with this form of art is found on a stone in the back recess. Newgrange was excavated by Professor M.J. O’Kelly during the 1960s and 70s.