It is a simple idea: take a hill or mountain of personal significance and see how many times you can climb it in 24 hours. For Christopher O’Brien, the hill in question was Allermuir, a 493-metre summit in the northern Pentlands overlooking Edinburgh.

Mad?

Certainly not.

You will not find incredulity here. Hill and ultra runners are the sanest people I know. The cliched tags of ‘mad’ or ‘crazy’ are lazy and ill-informed. Doing something hard is not ‘mad’; on the contrary, doing something easy is ‘mad’. Imagine having the gall to write to your mates: I’m going to run up and down Allermuir for 24 hours. Fancy joining me? Imagine having that confidence, that motivation, that self-belief.

Starting out at 6am on a day with the worst weather forecast of the week – high winds and rain – Chris left the car park at Swanston, summited Allermuir, then descended north, down a rough track that follows a fence line, skirts Todhole Knowe on a trod vandalised by the hooves of cattle, over a fence, down a grassy gully, over another fence, and then gently downhill to a post and dry stream at Dreghorn. He turned and ran the same way back to Allermuir, then descended to Swanston. Two ascents done, some 600 metres of cumulative height gain accomplished. How many more to go? Time would tell.

And that was perhaps the cruelty of Chris’ endeavour: this was the hill runners’ equivalent of a 24-hour track race. I have supported runners on Bob Graham and Ramsay rounds, routes on higher, harder hills than Allermuir; in these, time drifts – hours seem to vanish in the glory and challenge of the big mountains. The goal is to return to the start, not repeatedly like Chris, but within 24 hours. In between is a journey, not a conveyer belt of sameness. That sort of support is a different gig to running up and down the same hill. It seemed to me that Chris needed a psychologist for this one, not my banal patter.

I met him in the car park shortly after 8am. By chance, he was standing by his car, rifling through food and drink supplies. He had summited Allermuir four times, an overall height gain of Ben Lawers from sea level in his legs already. He was tired, he admitted. How do you respond to that? Give it a few hours, mate, then you’ll reevaluate your notions of ‘tired’.

Up, down, up, down, car park, up, down, up…

And then one of those potentially turning point moments that will occur in any 24-hour period. Chris reached across the wooden fence to touch the trig pillar, as he did every time, on the eighth summit when he froze as if electrocuted. He leaned against the toposcope, legs locked. ‘Cramp?’ He quietly nodded when others would have screamed into the wind. I pulled up the toes on his right foot, my hands becoming caked in the sheep turd embedded in his studs. Gently, he lowered himself to the ground, then lay back as if reclining on the warm sand of a beach. Was it over? I sat next to him, cross-legged on the summit of Allermuir, gazing at Chris and then down to Edinburgh, still tugging on his toes.

He slowly got moving again, easing himself downhill. I stayed quiet. It was for Chris to make the decisions. He must have been trying to rationalise what he was doing – or perhaps bargaining with himself: I will get to 10 summits, or 12 hours, or 20 summits. What is acceptable to me? The truth is nobody really cares. He lived a half-mile from the start. If he walked in before 24 hours were up, his family would not love him less, his friends not admire and respect him less. That is the power of these things – they are defined simply by your own level of personal satisfaction.

Another truth was that I really needed to get home. But when we arrived in the car park, there was no-one else there. I am sure he would have scoffed at the idea had I verbalised it, but I was resigned to keeping him company. It is only Allermuir, you might say, but leaving someone who is alone to be potentially incapacitated again by cramp in the cold and wind of a hilltop is not the way hill runners operate.

Up, down, up, down, car park. This time I left Chris; he had done 10 ascents in the first six hours. I went home and marvelled. As the wind blew unabated, he was still out there. As darkness fell, he was still out there. As darkness merged with a stinging rain, he was still out here, head-bowed, putting one foot in front of the other, touching the cold stone of the summit pillar. That is a story for him to tell. With a cavalcade of late-afternoon and night-time support, Chris would get to 29 – a number significant as it took him to the cumulative height gain of Mount Everest.

As runners, we take different things from being in the hills and mountains for 24 hours. One friend simply describes such activities as a ‘day out’ while others find profound symbolism in what is essentially running to get back to the very place you left. I am in the latter camp. We will talk about this for years: the day that bloke ran up and down Allermuir 29 times in 24 hours. And we will say, we were there.