The list of peaks is fixed by geology and revised by surveyors. Carnedd Llewelyn at 1,064 metres and Carnedd Dafydd at 1,044 metres anchor the northern half of the route, both deep in the Carneddau. From there the runners cross the Ogwen valley and climb to Glyder Fawr, recently remeasured at 1,001 metres, which earned the mountain a place on the official course only from 2011. Then it is over to Garnedd Ugain at 1,065 metres, and finally up to the summit of Snowdon, Yr Wyddfa, at 1,085 metres. Five mountains. Eight thousand feet of climb. A finishing pitch that drops the runners onto the highest summit in Wales, where weekend tourists who came up by train look on as exhausted athletes stagger across the line.

Ron James, the warden of Ogwen Cottage outdoor pursuits centre, dreamed it up in 1970 with Dr Ieuan Jones. Sixty people came to a trial run that first year. The first official race was held in 1971. In those days men started from the Conwy Bay shoreline at Abergwyngregyn and women started from the Ogwen valley, both finishing at the top of Snowdon and then descending under their own power, responsible for their own safety. The kit checks were strict. Boots had to be approved. Rucksacks had to weigh a minimum. The early entrants were mountaineers first and runners second. The British Army provided the checkpoints, and the West Bromwich Mountaineering Club sent a team every year. The race grew into one of the great endurance fixtures of the British mountain calendar.

Gavin Bland ran the course in three hours, twenty-seven minutes and twenty seconds in 1999. That stands as the men's record. Angela Mudge, in the same year, set the women's record at four hours, two minutes and thirty-nine seconds. To climb every Welsh thousand-metre peak in under three and a half hours is not running. It is something closer to flight. The team event, three best finishers' times added together, fell to the Reserves team of the Royal Regiment of Wales in 1996 at thirteen hours, forty-one minutes, fifty-six seconds. Twenty-five years later those records still stand. The course has not changed enough to make them break easily.

A fell-running class was added later, and so was a team event. The Gorphwysfa Club took over organisation from the military in the 1990s, and the First Hydro Company has sponsored the race for some years. The event sits at the harder end of British mountain racing. The Welsh 3000s, the longer cousin which adds all the peaks above three thousand feet rather than a thousand metres, is the standard challenge. The 1000 m race is the timed competitive version, the one where you find out what you can do against a clock and a course that does not care.

Ask the finishers and you get a range of answers. To stand on Snowdon at the end of a chain of summits you have climbed since dawn. To know that you can. To honour a friend who used to run it. To raise money for the mountain rescue teams who pick up the runners who do not finish under their own steam. The race rewards navigation as much as speed, and on a cloudy June Saturday a navigational error can cost an hour. The volunteers staffing the checkpoints have seen every kind of weather. They will see most of them again next June, and the runners will keep coming back.