It’s just past noon and I’m already tired. We’ve trudged relentlessly uphill since daybreak and there is plenty more to come. The thin, rarefied air has sapped our energy as we climbed through what could, in parts, be taken for bleakest Wales or wildest Scotland — a stony, green-tinged wilderness of valleys and ravines. When the clouds break I glimpse a vast snow-capped mountain range. Ahead, our guide clucked and cajoled the yaks. This is untamed Tibet at a very high and wheezy 4700m.

It’s another 500m to the pass, Shuga-la, and we are keeping an eye on each other for altitude sickness which can be fatal. We met a couple who had been forced to turn back. They had camped here and spent a miserable night with headaches, insomnia and delusions — all the classic signs of altitude sickness.

The Ganden to Samye trek is one of the more popular routes for foreign hikers in Tibet, mainly because there are significant attractions at the start and end and because travel between them is straightforward. Although relatively easy it is far from the teahouse cosiness of Nepal. There are no facilities during the three-or-four day hike, just a handful of villages which, at best, might provide a roof and an eager audience of fascinated and naughty children. Self-sufficiency — at least in food and a tent — is the key.

Ganden Monastery is one of the most evocative sights in Tibet. Founded in 1417 by a wandering monk, it became the main seat of the region’s dominant monastic order and home to thousands of monks. The upheavals and wanton destruction of China’s Cultural Revolution destroyed Ganden in 1966 and, until recently, it was little more than a ghostly shell. But Ganden, along with many other Buddhist sites, is undergoing restoration work. Cynics are quick to point out that it is tourist revenue not dubious religious freedoms that has enabled the monastery to rise again.

Whatever the arguments, it is a marvellous sight. The tiered monastry sits on a curved ridge, behind which lies the huge expanse of the Kyi Chu Valley which leads 40kms to Lhasa. Some of the best views can be had from a cluster of prayer flags higher up the hillside. These act as a magnet for pilgrims wanting more than the hour-long kora, or ritual wander, around the monastery.

We bedded down in a long, dusty room above Ganden’s only shop. Only an occasional murmuring and crash of cymbals wafting down from the chapels and halls broke the silence. Our first day on the trail was a gentle three-hour stroll to Hebu, a small village of flat-roofed stone houses. It is the only place to hire yaks and a guide, very useful for lugging your gear and provisions over two 5000m-plus passes. These animals make the difference, not just between pain or pleasure, but success or failure.

Our guide put us up in his tiny house in a muddy courtyard. His wife, mother and daughters slept next door in the kitchen, the larger and warmer of the two rooms. He joined us on the floor with his two sons for a cramped, but cosy, night.

Yaks are jumpy, frisky creatures and not keen on strangers and it took three attempts before our gear was loaded and secured on the beasts. It was a bigger struggle trying to keep pace with our guide and his son who, fitter and accustomed to the thin air, raced ahead. Much of Tibet’s scenery is deceptive.

It’s not so much the intense light and the clarity of the air distorting your sense of distance but more the fact that it often dosen’t resemble what “Roof of the World” suggests. Tibet is a plateau and is already high before most of the mountains rear up. And, except for the Himalayas bordering Nepal and India the mountains are often not as sheer or sharply defined as you might expect.

But, I thought to myself as I wheezed forward past boulders and tussocks of grass, it was still hard work. Nearing our goal the trail followed a wide incline, behind us a perfect U-shaped valley. At the pass we flung three stones onto the large landmark cairn, or la-dzay, in the way Tibetans do to give thanks for a safe journey.

Descending steeply into a narrow ravine, then crossing jumbles of scree on a precipitous path, we followed small and erratic cairns that pointed the way into and across a long grassy valley. In the distance, beyond the river, lay a nomad camp of yak-hair tents.

Nomads are one of the features of this trek and are particularly attracted to wet valleys that povide good pasture for their yaks and sheep. Unfortunately their ferocious dogs are hostile to strangers so a good stick is useful. It’s an unbearably harsh lifestyle fed, largely by, (for most Westerners) an almost inedible concoction of barley flour called tsampa. For the most part they are a friendly lot though clearly unused to foreigners appearing in their midst. Our guide coaxed a fire from sprigs and we cooked a meal of astonishing carbohydrate properties and little else. I have never been so grateful for a stone sheepfold but there we were, snug in our sleeping bags with its low walls cutting down the draught on a surprisingly mild night.

The following midday we reached Chitu-la, a little lower than the first pass, and said farewell to our guide and his yaks. They would return home that evening while we were still on the way to Samye. Our trail skirted the slippery, rocky shores of two small glacial lakes before plunging through a steep gorge and into forests that contrasted sharply with the open, exposed terrain of the previous days. A few nomads and snarling dogs dotted the way although there was little sign of their animals. We left them behind to camp at a sublime spot under a tree near a bend in the river.

It was a long, long haul down the Samye Valley on the final day. After a smattering of villages and hamlets amidst fields of barley and millet, the gleaming roof of the Utse, Samye’s main monastic building, finally shimmered into view. And in the very best traditions of hopelessly misjudging Tibetan distances, it remained a fustratingly long walk away.

The monastery is one of the oddest places in Tibet. Based on a temple in Bihar, India, its design reflects Buddhist cosmology. The central building represents Mt Meru, the mythical fount of creation which almost certainly derives from the existence of Mt Kailash nearly 2000km to the west.

The walled complex feels like a mediaeval village. Although people live in small rough houses with their cows stabled in little lean-tos it remains a religious centre. The Utse houses an assembly hall and a number of chapels while the rest of the monastery comprises a series of stupas, chapels and obscure buildings. It is as fascinating and absorbing as it is incomprehensible.

There is one more novelty on the return to mainstream travel — crossing the wide Brahmaputra River to the main road. Several long flat-bottomed boats make the 40-minute journey each day and as we slid through its grey-brown silty waters, I looked across to a dramatic wilderness of hills and mountains scarcely able to believe we had walked from way over there to here.