Bagging Munros in a weekend

OK, here's the theory. Catch a sleeper train from Euston Thursday evening. Arrive in the heart of the Scottish Highlands early Friday morning. Walk to Loch Pattack, set up camp and spend the next two days climbing Munros before returning on the sleeper Sunday night to arrive at Euston in time for work on Monday morning. A weekend of Munro-bagging in the style of the late John Smith, who I'm told regularly used a similar schedule to escape the pressures of Parliamentary life.

Perhaps I've seen The 39 Steps one too many times, but I've always thought there's a specific romance to the idea of a sleeper train. Unlike a plane or a bus, the sleeper offers the real promise of sleep as time travel, a kind of soporific teleportation complete with beds, pillows, sheets and blankets.

I'm not disappointed. After a couple of drinks in the train's bar we turn in, two to a cabin, in ship's berth-type bunks. There's even a tooth cleaning set with a little vial of water for rinsing your mouth.

In the morning the real magic of the sleeper is revealed. Duncan, our host for carriage M, wakes us at 6am with coffees, teas and Scottish shortbread. Half an hour later, the train pulls into Dalwhinnie on the edge of the Cairngorms national park. We soon find ourselves alone on the platform, the train a disappearing glint, a loch at our backs and the wilds of the Scottish Highlands opening before us. It really is a strange sensation. To be in a state of stillness all night as Britain passes you by. To dream through an entire country, half-woken by the occasional shunt of the engine, before being rocked back to sleep. Then, come morning, to find yourself in a new world to the one you closed your eyes upon.

We're soon brought back to earth. It starts to rain. A cold wind sings down the rails. The name of a derelict building opposite is picked out in rust where letters were once bolted to the wall: Dalwhinnie Hotel. To top it all we're not entirely sure where our route to Loch Pattack begins. What we do know is the site where we plan to camp is around nine miles away and that at this time in the morning the 90 litres each of us is carrying feels very, very heavy.

A plaque on the wall of Dalwhinnie station provides a moment's distraction. It commemorates the occasion of General Montgomery's visit to the village in May 1944 while he was planning the Allied invasion of Europe. Before boarding his train, The Rapier, he told the villagers of Dalwhinnie "I am grateful for having been left in peace and quiet and have enjoyed my holiday. Now I must go off and see if we can get this war finished." Briefly buoyed by this D-Day spirit and a full Scottish breakfast at The Inn at Loch Ericht, we set out on our way.

Three hours later, having traced the long ribbon of Loch Ericht past turreted lodges and accompanied by song thrushes and goldcrests, we break away from the shoreline and head north east into wilder country. Coming round the corner of a natural fir wood, we see Loch Pattack, flecked white by the wind whipping down from the mountains reflected in its surface.

One of the pleasures of wild camping is getting to know a specific area intimately, familiarising yourself with its peculiarities and characteristics. On our first walk, however, us and the landscape are just being introduced, and much of it is new to me, totally different from the walking I've done elsewhere in Britain. The thick bogs around the loch are broken up by peat cliffs, bone-white stumps of ancient trees protruding from their dark walls. A herd of long-maned ponies watch our progress, meadow pipits dart among the heather and sandpipers skim their wing tips across the surface of the loch.

We decide to try and bag our first Munro, Carn Dearg, that afternoon. The Munros are Scottish mountains over 3,000 feet, named after Sir Hugh T Munro, who first surveyed them in 1891 when he counted 236 such peaks. Advances in surveying methods now confirm 284 Munros. The Rev AE Robertson was the first man to climb them all in 1901, and since then over 2,500 other climbers have "bagged" the full set.

Veering from the path we begin our ascent up the steep shoulder of the foothills. The rain-soaked day has left the undergrowth remarkably colourful, the swollen cushions of purple moss and bright yellow fronds resembling the soft coral of a Pacific reef. Halfway up a couple of mountain hares break from cover and zigzag up the slope before us. A grouse explodes from the ground and squawks its low flight over the heather. The environment is at once grandly empty, bare hills nude of any adornment of walls or houses, and yet also alive with animal movement. When we reach the summit we see a herd of deer below, eyeing us, stock still, before trotting off over the horizon.

I say summit, but after a quick check on the GPS, it's confirmed that we are not actually on top of our first Munro of the weekend. That lies a couple of hundred feet above us in the thick grey cloud. The day, however, is drawing in, so we return to camp, having failed to get the "bagging" off to quite the start we'd hoped.

Another pleasure, if that's the right word, of wild camping, is the focus it imposes upon you in terms of your priorities. That night the rain keeps coming, and as a result how to keep dry and warm, keep the fire going and cook become the main objectives of our evening. Life becomes immediately simpler as a result. It's almost imperceptible, but it's that simplicity, that humbling under the elements that keeps us contented, despite the rain and the wind, in a way that is rarely experienced in the city. What I'm less happy about is the primary colours used for tent interiors. Why is that? I wake early the next morning, the sun shining through the yellow and green walls, reflecting off my red sleeping bag, feeling like I've come to in the studio of a kid's TV show rather than a far flung highland idyll.

After breakfast, we're back on track in earnest, walking out towards the imposing fortress of Ben Alder (from the Gaelic, hill of rock and water). It's one of Scotland's great remote mountains, a vast high plateau surrounded by steep corries. For us, Ben Alder offers the advantage of providing access to two other Munro peaks, Beinn Bheoil and Sron Coire na h-lolaire . The three summits sit along the ridges of a horseshoe range, and are a demanding ask of even the fittest of walkers. As one of our guidebooks says, tackling all three at once can feel "more like an expedition than a walk". So far, however, it's the Scottish Highlands 1 and us nil, so there's no turning back now.

The walk proper begins with our ascent of Leth-chas an Fharaidh, a dramatically precipitous ridge that looks like the shattered remains of a castle's battlements after months of siege. It ends 10 hours later with all four of us limping into our campsite as the last light drains from the day. In between, we've experienced the full range of mountain weather and terrain. From driving hail to hot sun; from bare, gentle slopes to vertical cliffs and cornices of snow; from acres of rocky, sharded ground, to mile on mile of thick flora. Similarly we've been through the full range of our own methods of movement, from marching along ridges, to scrambling up arêtes; at the summit we were even able to slide down patches of snow.

Once we're up, however, the views remain constant. Constantly stunning. For sheer grandeur of scale, the remote highlands can't be beaten. For most of the walk there is literally not a town or village in sight. Other mountain peaks rise everywhere, vague and ethereal on the horizon and the long lochs stretch off into the distance below us. At the very end of the walk, we see a lone stag silhouetted against a rainbow. It's such a perfect sight it feels like a benison, a nod of approval from the landscape, a reward for our day's walking in the wilds.

On our last night we experience what must be the most pleasing element of camping on a walking holiday, and that's simply staying where you've been all day. Rather than driving away, we're able to sit around the fire as a full moon rises above us and look back at what we've climbed, to marvel at the awesome beauty of the Ben Alder range, not with the anticipation and concern we felt in the morning, but with the tired satisfaction of having climbed it and two other Munros besides.

In the end that was our final tally. Three Munros, 45 miles walked and three days of conversation, because a walking break is also a talking break. When else do you get to spend 10 hours non-stop just chewing the fat with your friends? For me this has been as much a crucial part of the weekend as anything else, and when we arrive back in Euston at 7.30am on Monday morning, I'm sure it's as much this element of shared experience that sets us apart from the suited commuters as it is our sun burn, blisters and faint aroma of wood smoke.

· Owen Sheers' latest collection of poetry is Skirrid Hill (Seren, £7.99). His first novel Resistance is published by Faber at £10.99. You can buy it from the Guardian Bookshop