Marvel at winter solstice sunrise in NewgrangeIf you put your head on the floor of the burial chamber at Newgrange, Ireland's most famous passage tomb, rest your cheek on the soft grit and look back down the slightly wonky passage of upright stone slabs, you can see a wigwam of light at the end. This is the entrance, which faces south-east over the wide, shallow valley of the River Boyne and a ridge called Red Mountain.
If you are lucky enough to be one of the 50 people, plus partners, whose names were pulled out of a hat (or rather, a scale model of Newgrange) by local children in September, you will be in the tomb one morning next week, between Tuesday and Sunday, waiting nervously for the winter solstice sunrise.
If it's fine, the sun will clear Red Mountain at precisely 8.58am on each of these days, pour through a rectangular slot above the tomb entrance and hit the floor at the back of the chamber. Then, as the sun rises, the beam will slide back down the passage towards the entrance. By 9.04am the chamber will be dark again - and the most sought-after six minutes in the world of heritage tourism will be over.
It is 40 years since Professor J O'Kelly, professor of archaeology at University College Cork, saw the winter solstice effect at Newgrange for the first time. He was five years into a 14-year excavation and had heard tales of some sort of astronomical alignment. "Between the bright sky and the long glittering silver ribbon of the Boyne, the land looks black and featureless," he wrote. "...the direct light of the sun brightens and casts a glow all over the chamber."
Not only was the solstice discovery to make O'Kelly famous, it was also to have a profound effect on the Boyne Valley. Clare Tuffy, manager of the Brú na Bóinne Visitor Centre, which controls access to Newgrange and is run by the Office of Public Works, remembers the late 1980s as crisis point: ''We were getting up to 17,000 visitors a day, huge coaches were just turning up along the tiny lanes. There were no facilities, there was no parking."
That was just everyday access: people wanting to be in the tomb for the winter solstice had to apply to Dublin - and there was a backlog of thousands.
Eventually, Brú na Bóinne (usually referred to as "the Bend of the Boyne") became an archaeological park, then a UNESCO World Heritage Site in 1995. The visitor centre, a symphony of spirals and mounds in wood, glass, stone and concrete, opened 10 years ago on the south side of the river.
A small suspension bridge was thrown across the muscular brown waters, where those who originally settled Newgrange some 5,000 years ago would have speared salmon, and a minibus terminus built, from which visitors are ferried to the tomb or its larger sister at Knowth. In the year 2000, a lottery system was introduced for solstice places; this year, there were 28,000 applications.
Clare and I nipped over before the first group arrived. Only 650 people a day are allowed in the tomb - it must be one of the few tourist attractions in the world that is patting itself on the back for reducing visitor numbers - on a timed entry system: miss your slot and you miss your chance to go in. Turn up after lunch, whatever the season, and you probably won't get a slot at all.
All Irish passage tombs follow a similar pattern: a mound of rocks and soil, a retaining wall of kerb stones - often decorated - pierced by a single passage ending in a burial chamber, which at Newgrange is cruciform. Penetration by light so vividly symbolises fertility, the end of winter and the coming of new life.
We crunched up the passage, unable to avoid rubbing the slabs on either side - one reason, along with human breath, for restrictions on visitor numbers - and gazed at the three recesses, each furnished with a basin stone for human bones and small artefacts. The one on the right was one of the most beautiful stone forms I had ever seen: a soft cushion of pale granite with two gentle hollows, itself balanced on a more prosaic stone below. The walls were alive with chevrons, diamonds, spirals and a fern, all carved by stone tools.
Outside, beyond the famous spiralled entry rock, we shaded our eyes. The Irish Midlands are low-lying, but the mound commands sensational views. It would have dominated the valley, faced with glittering white quartz from the Wicklow Mountains, 30 miles to the south, dotted with black stones of water-rolled Mourne granite from the shore of Dundalk Bay, 60 miles to the north. It would have been a focus for those living around it. It continued to be so; later peoples built a pit circle and ringed the mound with standing stones. Early tourists - including the Romans - saw it as a shrine.
The Bend of the Boyne is where the river loops south en route to the Irish Sea, skirting the ridges upon which sit the three great tomb complexes - Knowth, Dowth and Newgrange - and about 90 archaeological sites altogether. The River Mattock, to the north-east, turns it into a virtual island, so the land was fertile, protected and settled by farmers long before Stone Age man started his 400-year construction of Newgrange, around 3,200BC. Over time the area became scattered with tombs, and was possibly planned on a huge scale.
The winter solstice, however, has made Newgrange a megastar, eclipsing all rivals. This year, to celebrate the 40th anniversary, a webcam will be in the tomb for the first time on December 21 and 22 (the solstice is technically on the 22nd, but the anniversary is the 21st) to record the passage of the sun. "If it's a clear day, people are so excited," says Clare. "But they never believe us about the timing. They always think they're going to miss it. They never do."
Boyne Valley Private Day ToursPick up and return to your accommodation or cruise ship. Suggested day tour: Newgrange World Heritage site, 10th century High Crosses at Monasterboice, Hill of Tara the seat of the High Kings of Ireland, Bective Abbey and Trim Castle the largest Norman castle in Ireland More ...