there it is, can you see it?" Our little group is standing on the Cairngorm plateau, 500m above the Coire na Ciste ski centre car park.

It feels like being on the ceiling of Scotland here, with mountains bobbing away into the distance behind us like silent waves. But for now, we are not looking at them, we are squinting at the jumble of boulders ahead of us on the hillside on the north of Cairn Gorm that plunges into Strath Nethy, trying to see something, anything, that could possibly have been built by human hands. Nothing.

Our guide Patrick Baker, mountaineer and author of a new book on the forgotten history of the Cairngorms, tries to point out the secret mountain shelter known as the El Alamein, but all we can see is a field of rocks frozen in a downward tumble. It took Patrick two attempts to find the El Alamein during his research - the first time he spent an hour walking up and down just 20ft above it without seeing it - and it's hardly surprising. The refuge is so elusive that it has achieved almost mythic status in mountaineering circles, heard of but never seen, like a legendary beast.

Then the hazy midday sunshine illuminates a huddle of pink granite. "Is it that heap of rocks?" someone asks, struggling to be more specific. "Yes, exactly!" says Patrick, setting off towards it. How on earth has anyone ever found it in mist, fog or snow? We follow, clambering over 6ft boulders towards this strange little cairn. Looking at it perched on a near-precipice on a route to nowhere (there is no sign of a path as far as the eye can see), it has to count as one of the most eccentric structures in the Cairngorms. But the point about that El Alamein is that it isn't even meant to be here. It was supposed to have been dismantled decades ago. A decision was made to pull it down, not because of its appearance or even its bizarre location, but as a result of an anguished debate that took place following the worst tragedy in Scottish mountaineering history.

How benign the weather is up here on this sunny April afternoon; how very different it was on Saturday, November 20, 1971, when two parties of Edinburgh teenagers headed up into the mountains from the Coire Cas ski station car park further round the mountain. Each led by a young instructor, the two groups were due to spend the day scaling Cairn Gorm and Ben Macdhui, learning navigation skills and experiencing the wilderness of the plateau, before descending onto the Lairig Ghru (the famous Deeside to Strathspey hill pass) and spending the night in Corrour Bothy there.

The weather in the Cairngorms is notoriously fickle, but that afternoon a storm of unusual ferocity set in. First the winds picked up and then a dense blizzard tore across the plateau. The two parties, travelling separately, each made the decision to abort their mission and make instead for emergency shelter at the Curran Bothy, one of several basic shelters put up on the plateau over the previous 20 years. But only one of the groups made it to safety there, having to dig out the door to get in. The 21-year-old instructor leading the other group knew the bothy would be hard to find in the snow so opted to hunker down in the bed of the Feith Buidhe burn on the exposed moor instead. A difficult situation then became desperate as the weather worsened and the party was forced to bivouac outside for not one, but two nights. During those agonising hours, the children became buried in snow. When the party was discovered on the third morning, poignantly close to the Curran Bothy, five of the children and an 18-year-old assistant instructor had died.

The incident brought home in the most terrible way the dangers posed by Scotland's most famous mountain range. A fatal accident inquiry into what became known as the Feith Buidhe tragedy did not apportion blame, but it did trigger an impassioned debate about mountain shelters, around a dozen of which were at that time scattered around the Cairngorms. While some saw them as essential emergency shelters which could save the lives of those caught out in bad weather, others argued that their very existence lulled the unwary into danger: they would seek them out when weather deteriorated, and in the featureless landscape of the plateau, especially in deep snow, might never find them. In the end, the decision was made to dismantle the three high level Cairngorm huts, the Curran, St Valery and the El Alamein, but while the first two were destroyed, the El Alamein still stands, forgotten and unused.

The El Alamein was built by the 51st Highland Division in 1963, named after one of its most famous battles. As the crow flies, it is hardly any distance from the hive of activity at Cairn Gorm ski station. During the steep upwards climb to get to the shelter, we have clear sight of the season's last determined skiers just a couple of kilometres away on shrinking snow fields.

Hardly anyone comes in this direction, though: the path, such as it is, fizzles into nothing when the gradient flattens out at the top of the ascent. There, bam, the wind hits us like a water cannon. This is a landscape of cushiony sphagnum moss, the precursor of peat, and dark green succulent club moss; a pair of ptarmigans is the only sign of life besides us. Behind us, the vast green blanket of the Rothiemurcus Forest envelops Loch Morlich but ahead of us, looking over the plateau, there is nothing, but nothing, to impede the elements and only the occasional granite tor to provide navigational aid. Imagine being here in whiteout conditions, Baker shouts to me through the roar of the wind, you could easily get completely disoriented.

He knows all about the weather up here. Baker, 39, an investment writer for an asset management company, has been captivated by the area since first visiting in his early 20s. In spite of being diagnosed at 20 with hereditary spasticity paraplegia - a rare, progressive neurological condition affecting his lower limbs that doctors said would likely leave him unable to walk eventually - Baker has managed to maintain a high degree of mobility and continues to undertake impressive solo expeditions, often involving arduous climbs, though he does less ambitious journeys now than he once did. He describes his condition as a good motivation to "explore as much as I can while I can".

He notes that the highest wind speed in the UK was on the top of Cairn Gorm - 176mph, recorded in 1993 - and that the lowest temperature, -27.2, was at Braemar, the area's inland position making for greater extremes than in Snowdonia or the Lake District. However, Baker feels that the "hidden narratives" of the Cairngorns - which are the size of Luxembourg and contain Britain's second to sixth highest peaks, have been largely overlooked. So drawing on "out-of-print books ... online chatter ... and drunken anecdotes", he set out to find the Cairngorms' forgotten stories, from the bucolic settlement built by an 18th-century aristocrat, to the metaphysical phenomenon known as "the Big Grey Man", when lone mountaineers describe a chilling sense of being followed even though there is no-one for miles around.

The force and caprice of the weather is alarming enough on its own to be the subject of numerous tales among seasoned climbers. Baker quotes one of his favourites, mountaineer WH Murray, talking about the frightening experience of being caught in a blizzard on the Cairn Gorm plateau with a companion in the 1930s: "Below, above, on all sides, was the impalpable writhing whiteness, which left the eye nothing to focus on, nothing to which one could relate one's own body . . . We had the sensation of floating rather than walking."

It was in theory to assist such climbers that the shelters were constructed in the 1950s and 60s, adding to some pre-existing Victorian structures, though the location of the El Alamein is odd. Striking out across the plateau, we start to descend gently towards Strath Nethy, with the high ridge of Cnap Coire na Spreidhe looming ahead of us to the right.

When we finally reach the bothy, precariously close to a sheer drop, it turns out to be a structure of remarkable sturdiness, with a concrete base and heavy iron panels forming a frame and apex roof. Measuring around 3ft x 6ft inside, and just tall enough to stand in, its walls are made from granite boulders plugged without method into gaps in a grid framework nailed to the frame and covered with thick hessian. The heavy iron door, now hanging from one hinge, would once have provided essential protection from the wind, which is today blowing directly through it. It has not been maintained in decades, and the roof is open in several places, but still provides a remarkable degree of shelter, and peace.

In his book, Baker describes arriving there alone: "It reminded me somehow of a grotto, a deliberately conceived place of reflection and veneration."

Those who have used the bothy have left no visible trace, aside from the word "welcome" scored into the iron door. It has probably rarely been used, Baker reflects, but he can't help hoping it survives another few decades.

"If you were to see something like this being built on the hillside today, you would be appalled, but because of its antiquity, you have this reverential feeling for it. I would hate to see it removed."

He reveals that it was mistakenly sited here due to confusion over grid references. It was meant to be up on the high plateau, not tucked it away en route to nowhere on this rocky eyrie. That was what saved it.

This shelter is no longer robust enough to protect walkers from a mountain gale. But as we leave, pointlessly pushing shut the door, it feels as if we have completed a pilgrimage, commemorating an earlier, more unsuspecting era of mountaineering.

The Cairngorms: A Secret History (Birlinn, £9.99) is published on May 15