A long descent from the hills north of Rawalpindi brings us to the valley of the Indus. The first glimpse of this great river which is to be our companion for the next fortnight brings a sense of romance. Its brown water shines in the afternoon sun, glacier-fed with silt from the heart of the Himalaya and Karakoram and charged with the history of millennia.

For three days the Indus leads us through a deep gorge, while high above it the Karakoram Highway roller-coasts on ledges blasted from the rock. This is the collision zone of India and central Asia, where Earth's crust pushes up faster than glacier and river can wear it away. The landscape is vertical.

It's also beyond reach of the monsoon. Parched slopes with a scatter of wiry scrub and grey weeds reflect the heat like an oven. Flat-roofed mud and stone houses and incredible terraces of corn irrigated by races from side torrents cling to the mountains a thousand feet above the river, whose water rushes uselessly past in the depths of its gorge.

Late on the third day the Indus swings east and its valley opens in desolate magnificence, as bare of vegetation as Mars. In Shatial village, a shouting rabble of small boys guides us down a dirt track to the rest-house and festoons our courtyard railings while we mend the days' punctures and try to cure our white spirits stove, ill from a diet of Pakistani fuel. The place has plumbing and wiring but no water or electricity. At bed-time the manager curls up on the floor in his blanket with his Chinese-made AK-47. It has a full magazine.

As we pedal eastward next afternoon a prodigious snowy massif appears ahead, glowing pink in the last of the sun: 8125m Nanga Parbat, eighth highest mountain in the world. To see it at close quarters we take a heart-stopping jeep ride from Raikot Bridge to Tato, on a track blasted from the mountain and supported on shaky rock walls. Tato village is a snow-melt oasis in the floor of a canyon 1300m above the Indus. Two and a half thousand people live here through the summer growing corn and potatoes. It seems incredible that produce from this speck of greenery should be exported in jeeps down the bare desert mountain and loaded into trucks for Islamabad. When snow covers the village people with land in the valley retreat there. Those who spend the winter in Tato, we're told, just "eat, shit and sleep".

Two hours' walk, to 3500 m where breath is short and a light-headed feeling sets in, brings us to Fairy Meadows. Once a glacial lake but now a swampy hollow rimmed by moraine forested with pine, juniper and birch forest, its view of Nanga Parbat is sublime. Fairy Meadows was named by German climbers whose expeditions, after great loss of life in the 1920s and 30s, culminated with success in 1953. With what relief they must have returned to trees, pasture and running water after weeks on ice and snow!

We wander the alpine meadows, then return to the turbid, rushing Indus in its barren trench.