Per the Newgrange website, generations of archaeologists have been working to uncover the secrets of the passage tomb: the methods of construction, how and why it came to be positioned, and why its creators chose the distinctive “kidney-shaped” design. According to National Geographic, one such mystery was finally unraveled in the 1960s, when experts uncovered the meaning of the tomb’s “roof-box,” a “baffling orifice” found above the entrance to the tomb’s central passage.

Professor Michael J. O’Kelly was the archaeologist in charge of excavation and restoration at Newgrange between 1962 and 1975, according to the Newgrange website, and it was in 1967 that he made a startling discovery: the roof-box had been specially positioned to light up the tomb passage leading to the site’s ancestral remains on the shortest day of the year, winter solstice. His discovery was a reminder of the incredible ingenuity of Stone Age engineering, and of the hidden secrets that can still come to light millennia after such seemingly humble structures were built.

In 1993, Newgrange was declared a UNESCO World Heritage Site and continues to attract tourists from around the world.