The clouds are black, pile-driving over the hills and spitting cold rain in our faces. We're standing in a car park on the edge of Dartmoor, trying to get changed into running gear before it starts to pour.
"OK, let's do it," says Ceri Rees, our guide and leader.
I've come to Devon for a new Wild Running weekend, a 26-mile scamper across one of England's most desolate landscapes, rarely using footpaths. The plan is to break up the exertion with a night in the middle of the moors in the rustic-but-charming Powdermills Bunkhouse (shared rooms, sleeping bags – we don't want to get too comfortable). For those too tired to get the train home on Sunday, the trip ends with a night in the cosy Rock Inn in Haytor.
By the time we arrive at our starting point in South Brent, the day is already almost out of light.
We set off in single file into the woods, sloshing along through mud and streams for about 15 minutes before we emerge on to open moorland. The ground is so uneven that I don't get chance to look up until we're high above the Avon dam. Suddenly the wilderness is all around me, silent in the fading dusk. It will soon be completely dark, yet on we go, further into the moor, like a group of escaped convicts running for our lives.
"It's time for the torches," says Ceri, stopping at last. A former international athlete and the founder of Wild Running, he's obviously finding this easy. The rest of us are puffing hard.
With our head torches on, everything changes. Instead of the vast, empty moorland, the world is reduced to a tiny circle of light right in front of my feet. I follow it, skipping over the rocks, listening to the splat-splat of the other runners; everything else is black, invisible.
I've no idea how Ceri knows where he's going. He doesn't stick to the trails, but heads straight through the gorse bushes and swamplands, only occasionally finding the relief of sodden grass to run on.
Running up hills is particularly disorienting. With no way of gauging how far up they go, you just have to keep pushing, pounding on as though in a dream, watching the ground rushing through your circle of light. As we head up one hill that seems to go on forever, I begin to feel suddenly lighter, as though I'm taking off, shedding my leaden body. Belatedly I realise what has happened: I've crested the hill and am now running downwards.
As we head back through the woods, I begin to fall behind. I'm taking it carefully. The rain flicking in the torchlight distorts the little vision I have, as does each exhalation, my breath momentarily clouding my sight as it gets caught in the light. We've just passed a place called Bloody Pool. I'm not taking any chances.
Ceri drops back to check I'm OK.
"One of the two rules of Wild Running is never apologise for going too slowly," he says, reassuring me, before hurtling off over the invisible rocks back to the front of the group. (The other rule is never to ask more than twice how far there is to go.)
After the first day's 12-mile run, I'm relieved to be in one piece, but buzzing with endorphins, my stomach burning with hunger. Which is just perfect, because our reward is an evening at the nearby Riverford Field Kitchen.
Eating at this organic farm, surrounded by fields, would be a delight at any time, but after a seemingly endless run through the wilderness, the spread it offers feels like the finest feast ever prepared.
There is only one dining time, 8pm, which has to be booked, and everyone in the restaurant eats together at long, communal tables, as plate after plate is brought out and passed around. Soon the table is overflowing with wholesome dishes made mainly from produce grown or reared on site. We tuck into beetroot and fennel gratin; leek, spinach and celeriac pie; and dark chocolate and almond cake. Sated, we retire to bed, only half-thinking about the next morning's 14-mile run.
The day dawns bright and still, but by the time we start running, back across the moor, the clouds have gathered again. With the benefit of daylight, however, everything seems much easier and my legs soon fall into a rhythm, knocking off the miles at a steady pace. Ceri seems to have a sense for when I'm tiring and takes quick breaks to point out sights, such as the impressive boulders jutting out of Haytor or the roadside grave of Kitty Jay, a poor orphan girl who killed herself in the 18th century after an ill-fated fling with a farmer's son.
And then on again we go towards our final goal, the Rugglestone Inn in Widecombe-in-the-Moor. Again my stomach is rumbling delightfully at the thought of food, perhaps too much, because with two miles to go I start to push the pace, surging passed Ceri. He quickens his pace, too, and before long we're racing along, skipping through puddles and leaping over rocks. It's a childlike joy, and I almost want to whoop. But then I slip, and tumble.
Unfortunately the story has a sad ending. We make it to the Rugglestone Inn, where the staff bandage up my gashed knee and feed me yet another glorious meal, along with copious amounts of ginger beer. But the night ends in A&E, with three stitches.
Wild running is a joyous, exhilarating way to spend a weekend. If you're training for a marathon or an ultramarathon, it's a world away from the monotonous pounding of city pavements. It's also a unique way to explore some of the wildest scenery in England. But whatever your reason for joining in, my advice is don't attempt to race Ceri to the finish, no matter how all-consuming your hunger.
• The trip was provided by Wild Running (07773 560335, wildrunning.co.uk). Weekends on Dartmoor or the South West Coast Path cost from £100pp (depending on size of group) plus accommodation (from £15 a night for a dorm bed to £89 for a double at the Rock Inn). Upcoming dates are 4-5 May, 8-9 June and 29-30 June; bespoke trips can also be arranged
Adharanand Finn is the author of Running With the Kenyans (Faber and Faber, £8.99). To buy a copy for £7.19 with free UK p&p, visit guardianbookshop.co.uk
