In this extract from his new book The Wild Swimmer of Kintail, following in the footsteps of postwar poet Brenda G Macrow, outdoor writer Kellan MacInnes goes skinny-dipping near the summit of Sgurr nan Ceathreamhnan, one of Scotland's remotest Munros.

Grey-white cloud blankets the heights of Sgurr nan Ceathreamhnan and I reckon the mist will be just brushing the surface of the water in Coire Lochan. The burn tumbles out the corrie, down a staircase of white-water steps and dark, boulder-fringed pools. I'm beginning to rather regret not having told anyone where I was going. I know! What were you thinking of? A remote area like this and all, but I just thought of the walk to Coire Lochan as being a walk up to a loch.

But now as I approach the cloud level I register what I already know, that Coire Lochan lies at 770m, at an altitude higher than some Corbetts. When I'm climbing a Corbett alone or with the dog I always send a text or leave a note with details of my route so someone knows where I'm going. But now I'm thinking no-one ever goes up to Coire Lochan except, judging by the tyre tracks on the ground, during the stalking season. Ninety-nine point nine per cent of Munro baggers are gonnae approach Sgurr nan Ceathreamhnan from the Glen Affric side. Aw fuck, dinnae break yer ankle up here! Could be days before anyone realises I'm missing. Aw naw, remember those bits about 'Safety on the Hills' you included in the appendix of Caleb's List. Think of the headlines: 'Writer of Mountaineering Guidebook Rescued After Failing to Follow Own Advice.'

I'm a born worrier. On the other hand, there is always, on the few occasions I've walked on my own in the mountains without anyone knowing where I am, a sense of freedom, a sense of self-reliance. It's all down to me now so I'd better not fuck up. It adds a certain frisson. If I break my leg, will I get a signal on my phone and be able to call mountain rescue from up here in Coire Lochan? Almost certainly not. I do carry an emergency shelter, a tiny one-man tent without a groundsheet so I reckon I could last a few days up here. Hamish Brown didn't tell people where he was going when he made the first ascent of the Munros in one expedition. Sure he had pre-arranged rendezvous points with friends and family and if he'd failed to show up they would have alerted mountain rescue but his rendezvous points were days apart.

Likewise, no one knew where Brenda G. Macrow was when she headed up into the hills around Glen Elchaig in 1946. But then if you'd just survived working on a USAF base during the Second World War, the risks of climbing Sgurr nan Ceathreamhnan in an old overcoat with some crowdie sandwiches stuffed in the pocket and only a Skye terrier for company probably didn't compare with dodging bombs and V2 rockets.

I plod on up towards Coire Lochan having resolved to walk very carefully and not slip and twist my ankle. Looking north I realise I am almost level with the summit of 730m high Carnan Cruithneachd. The loch must be here somewhere. No, there is another rise waiting to be climbed, leading to an upper, upper corrie. I tramp on, passing a little gorge with a white-water burn which seems to flow down out of the cloud from the very summit of Sgurr nan Ceathreamhnan.The gorge is like the Falls of Glomach made in miniature, high up on the mountainside. The climb up into the corrie is turning out to hold far more interest than I had expected. Looking at maps in the caravan at Dornie, I'd expected a tedious plod through heather and peat hags up to a dreich, wee loch. But the climb up to Coire Lochan is proving to be anything but and on a hot summer day I think it would be fun to explore the little gorge with the waterfall and swim in the pools.

Then suddenly, in a grassy hollow, I come upon death on the mountain. One of the saddest sights I have seen in nature. I catch a glimpse of a hoof and a leg, sticking up out the long grass. A dead hind, not unusual in the hills, at least she'd died high on the mountainside, not hit by a car on the A87. Up here in the corrie just below the west summit of Sgurr nan Ceathreamhnan would not be such a bad place to die. I can think of many worse places to die than up here. But something draws me on to look into the hollow and there I see the saddest of sights. The hind, I realise with a twisting in my stomach, must have died while calving. The hind must have climbed up here, to this remote corrie, to give birth. The head and neck of a calf protrude from between the back legs of the hind. The dead calf's mouth still open, a red orifice frozen in its first and last gasps for breath. I turn my face away and walk blindly on up the hillside.

Macrow 1946: We found the elusive Coire Lochan (2,500 feet) tucked cunningly away in a cloud-filled cleft—a little pool almost the shape of a star…

I'm nearly into the mist when, at last, at the top of a final grassy rise, there in front of me, like a sheet of rippling grey steel lies the elusive Coire Lochan. The mist hangs just 50 feet above the water but there is a brightness, sunlight, cutting through the low cloud. Boulder-strewn slopes of grass and scree sweep up to the west top of Sgurr nan Ceathreamhnan, somewhere up in the clouds. Three sets of antlers watch me from high up on the east face of the corrie. The lochan lies at 770m, higher than the summit of Suilven and it feels about the same temperature as on a Scottish mountaintop. I take off my rucksack and walk to the edge of the lochan. The water is black and peaty but I can see smooth stones on the bed of the lochan. It looks about two feet deep here at the edge.

'Got to do it, mate,' says a voice in my head, 'It's why you climbed all the way up here.'

Effectively I'm on a mountain top. The temperature is what… five degrees? I'll get hypothermia. A new headline flashes in front of my eyes: 'Little Known Scottish Writer Froze to Death Skinny Dipping on Remote Munro.'

'Got to do it mate,' says the voice again and I bend down and begin to unlace my boots.

The short, deer-cropped turf feels cold under my bare toes as I pull my fleece and T-shirt off then unbuckle the belt on my Rab trousers. I'm wishing I'd worn a better pair of pants though. These ones are definitely not 'pulling pants.' They're definitely 'caravan pants.' Caravan pants I hear you ask? Yip I keep a separate set of clothes at the caravan. My caravan wardrobe consists mainly of Umbro T-shirts from Sports Direct and hoodies from Primark. The idea is to minimise the amount of stuff I have to take with me. There are caravan shoes and socks too and of course caravan pants. The problem with caravan pants is that they're a collection of like all those pants you bought that weren't quite the right size but the shop refused to take back. Or those ones that shrank in the wash or those leopard skin CKs that were briefly fashionable about eight years ago or those cheapie blue Lonsdale ones from Sports Direct you never really liked. You know what I'm talking about guys!

So now I'm stood there on the shore of Coire Lochan in a pair of black Calvin Klein briefs that are kind of washed-out and faded and a bit small for me. What the fuck! It's pretty unlikely I'm gonnae meet anyone up here. It's only the deer over there among the boulders and scree who can see them and they're coming off now anyway. Woo hoo! I wade across the smooth, weed-coated stones and stand there in the water and raise my fists and shout: 'Yes!'

Naked under the mountain, I crouch down in the icy water. I just typed that but actually it wisnae too cold. I kick my legs and do a few splashy strokes of back crawl. Then I stand up. The mist drifts across the north ridge of Sgurr nan Ceathreamhnan. I look down. My willy looks very small and shrivelled.

'Got to get your hair wet, mate,' says the voice.

So I swim a couple of strokes on my front with my head under the water. Then I wade back out and stand on the grass. I feel brilliant. I've always been into a wee swim in a Highland burn on a hot July day coming down from a mountain. I knew other folk went swimming on days when it wasn't sunny, on days when it was grey and cloudy and cold, raining even, but for me it had to be a hot day. But standing there with the mist swirling over the west peak of Sgurr nan Ceathreamhnan I totally get it now. I totally get why they do, why they go wild swimming. I raise my clenched fists again then reach for my Paramo jacket and start drying myself.

The sun has come out. The mist has lifted from the tops. Dressed, sitting on a flat boulder beside the lochan, eating a sandwich and a bag of crisps. I've got my furry hat with the ear flaps on because I'm worried about getting hypothermia. But I'm not cold. My skin tingles under my down jacket and I feel great, rejuvenated, refreshed, ready for the long tramp back to Carnach and my bike. Unfortunately the karma wisnae set to last...

Kellan MacInnes, author of the acclaimed mountain memoir Caleb's List, Climbing the Scottish Mountains Visible From Arthur's Seat is back with a new book and a new challenge: wild swimming 28 high-altitude hill lochs in Kintail, a remote and mountainous area of the Scottish Highlands.

In The Wild Swimmer of Kintail, a life-affirming tale about the healing power of wild swimming, Kellan is walking in the footsteps of the little known 1940s poet, mountaineer and pioneer of wild swimming, Brenda G Macrow, who spent six months exploring the Kintail hills in the summer of 1946.

The Wild Swimmer of Kintail is available from Rymour Books, Amazon, Waterstones and all good bookshops.