A 5,200-year-old passage tomb older than the pyramids and Stonehenge, built by Stone Age farmers around 3,200 BCE. The kidney-shaped mound spans 85 metres and is ringed by carved kerbstones; inside, a 19-metre passage leads to a cruciform chamber. Once a year — at sunrise on the winter solstice — light enters a precisely cut roof-box and floods the chamber for 17 minutes.

Part of the Brú na Bóinne UNESCO World Heritage Site along with neighbouring Knowth and Dowth. Entry is by guided tour only, departing on shuttle from the visitor centre — you can’t drive to the monument.

Pro tip: the winter-solstice access is decided by a public lottery each September (free to enter via the OPW website). Year-round, a simulated solstice illumination is part of every standard tour.