There is a vicious simplicity to the snaking line of summits that make up the Welsh 3000s. This is hallowed turf and rocks: Crib Goch, the roof of a nation, the rock-desert of the Glyders, Tryfan, the quiet, high mountains of the Carneddau.

It is a classic: an undertaking that is long and arduous, but eminently doable for the determined hill walker or runner.

I had waited three decades, having first climbed Crib Goch and Snowdon in my early teens, with the knowledge of the Welsh 3000s lodged in my consciousness ever since. It had just not happened. My gaze turned to Scotland; another possibility would intervene; the time was never right.

The time is never right though, is it? And so: Boxing Day, a weather window. Maybe now, finally?

Under the cold moon, minutes before the sun blasted a blazing retort, poised atop Crib Goch, I set off from what could not be a slower start line, but with a firm objective: a midwinter Welsh 3000s.

But not ‘winter’.

Wind chill several degrees below freezing, the summit of Yr Wyddfa smeared in ice, but still not ‘winter’. It was seasonless, I suppose; it just happened to be midwinter, the day after Christmas Day. Another month, another day, another hour even, everything might have been different. It is that variability that keeps luring us back to mountains.

As for today, the mountains, in part, were liquid in form. I do not know how violently the saturated slope to Nant Peris angles. (If you are necessarily travelling direct, there is no easy way to Nant Peris.) Where the contours concertina, the land seemed to swell beneath my feet, a frigid slush with nowhere to go. A well-worn pair of Inov8 Roclite were thoroughly unsuitable.

At least there is a soft landing on waterlogged grass. Above 900 metres, on the Glyders, mist lolling, disguising what I thought I knew, landings were less generous. The world was slimy and slippy, and every step purposeful, deliberate. On the highest boulder on Glyder Fach, perched on a stack of other massive boulders, I lost my nerve for a moment, imagining myself sliding into one of the chasms between these great rocks. I stumbled on, more moving than running, very steeply downhill to escape the Glyders, then blundering into dead ends on Tryfan, and thereafter carefully descending again, flip-flopping between what seemed the least worst option at the time, a greasy, steep, unrelenting stairwell or the ramps of slidy grass either side.

At this stage during these things, there is an awful near-inevitably: it is going to get worse. For good reason in the Welsh 3000s. From Ogwen, the route climbs 600 vertical metres to a third set of mountains, to Pen yr Ole Wen, the western outlier of the Carneddau. I was fatigued and nauseous, very conscious that night would soon overtake me, but there is nothing unusual in that list, and at the summit it was clear that clag had not claimed these hills. They were mine. I ran on, feeling fine – brilliant would be the wrong adjective; I doubt I looked brilliant. But it was midwinter on the Welsh 3000s. I had been moving for eight hours. There were two vertical miles in my legs. Fine, in this context, feels like absolutely brilliant. Fine and flying.

Night came quickly on Carnedd Llewelyn: a ghoulish half-light on a still, rime-smeared summit. Beyond, now reduced to smudged outlines, were the final three summits of the Welsh 3000s. These mountains are a sorry denouement to the brutal spectacle of what has passed: rolling bumps of grass and moorland, topped unhelpfully by a mess of skiddy boulders.

A serene, breathless half-hour passed, nonetheless, pushing forward into torchlight, a moon that I had seen vanish at sunrise remerging to claim the sky, the lights of the North Wales coast a long way away, down there. Soon, almost too soon, it was over, and I rested a hand on the Foel-fras pillar, pausing in the cold, dark air, grateful for what had passed, eternally grateful for mountains.