Near the village of Stenness, a strange conical hillock snouts from a grassy field. Shrouded in rough grass, and encircled by a ditch, it is both a part of the landscape yet unmistakably artificial. This is Maeshowe, a 5,000-year-old chambered cairn, best visited at this time of year, when the days are at their shortest and the genius of its neolithic creators might be viewed to full effect. Inside, at 2.30pm, a crowd of strangers stand together in the gloom, waiting for something to happen. We discuss the cairn’s construction – the long, low passageway that leads into the dark, the great slabs of stone tightly corbelled to create the arching roof – and the runic graffiti scratched into the walls in the 12th century by Viking raiders. These runes are slender, branching figures, though their content is similar to what you might find in any bus shelter: who Thorni was bedding, adjudication of the shapeliest widows, who woz ’ere in 1153. Outside, the sun is dipping below the Hoy hills, casting long shadows. We lapse into silence, watching the warm yellow light seeping up the passageway. And then I spot it, what we are all here to see: a pencil-thin band of light appears on the far wall and begins to spread and strengthen, claiming the stone inch by inch until it forms a square window of gold, like a portal into another world. This eerie illumination can be witnessed only on the days around the winter solstice, when sunset comes into line with the stone entrance. The full significance of the cairn’s astronomical alignment is not fully understood, but the passing of midwinter must have been of great significance to our ancient predecessors – as it is for us. Winter here is long and dark and wet. On a clear night like this, one might hope to catch a glimpse of the northern lights in its dance of the green veils. But more often we are clouded over, wrapped in a blanket bearing rain and sleet. The bright days of spring feel a long way off. But the light show at Maeshowe promises they are on their way.