Sarah Shuckburgh takes her life into her hands on the main highway in Ecuador, where the driving is almost as dramatic as the landscape.

The Pan-American Highway is Ecuador's pride and joy. Few Ecuadorians own cars, but the 600-mile-long Panamericana is a sought-after address, a symbol of progress and modernity linking this tiny country with Alaska and the southern tip of Chile. For my husband Guillaume and me, desensitised by British motorways, the thrill of this bumpy, potholed road is that it leads through some of the world's most beautiful scenery.

At first, driving is alarming - pick-up trucks roar by, with extended families bouncing about in the back - mothers feeding infants, and older babies standing up, their tangled hair blowing in the wind. Buses, with passengers clinging to the roof, overtake on blind corners, hooting furiously and belching black exhaust. On the parched verges between ramshackle settlements, Indian women in woollen skirts and shawls bend double beneath bundles of sticks; other villagers herd a few sheep or milk skinny cows, or stare impassively from the shade of a tree. Giant agave plants spout 15-foot flower-stalks from clusters of pointy leaves. Beyond lies an immense landscape of steep-sided volcanoes.

We cross the equator, and continue north to Otavalo, a jostling town famous for its craft market. Otovaleña women wear woven blankets on their heads, long black skirts and dozens of gold necklaces. The men wear white trousers, ponchos and dark felt hats. Everyone has incredibly long hair - the women with thick plaits to their knees, and the men with glossy ponytails. They stare pityingly at our tousled, mousey locks and shapeless clothes. But everyone is impressed by our hired car, a gleaming Chevrolet 4x4 - far grander than our battered runabout at home, and uniquely luxurious here. Whenever we stop, it attracts crowds of admiring onlookers and hopeful thieves, whom we entertain (inadvertently) with piercing blasts of the alarm.

From Hacienda Cusin, a romantic highland hotel, we explore a mesmerising terrain of rugged, green-grey slopes, lush valleys and cloud-covered peaks. Air-plants cling to electric cables in the humid air, and vivid hummingbirds dip and hover in the hedgerows. Volcanic lakes of deep blue water shimmer against dramatic mountain backdrops. In one typical, isolated hamlet, we hear crackly music, and come upon a lorry selling fruit - from which two women are struggling with a bunch of bananas as tall as themselves. Pigs sprawl with their piglets in the road, and scraggy chickens and turkeys peck the dust. We stop to chat to some children - barefoot, grubby-faced boys with ponytails, little girls wearing ankle-length skirts and shawls, who speak Spanish as basic as mine.

We enter cloud forest, misty and mysterious, with tangled foliage, pampas grass and giant gunnera, home to woolly tapir, puma and Andean spectacled bear. Higher still lies tussocky páramo - a sponge-like habitat of moist grassland, dotted with flowers and strange gorse-like bushes, specially evolved for insulation against cold winds and harsh light. The highland weather can change without warning - skies darkening from turquoise to indigo, bringing sudden torrential rain. Minutes later we drive on through deep puddles, the volcanoes glistening dramatically in the bright equatorial sunshine.

On one highland track, we come to a makeshift road-block. A toothless, wrinkled face appears at my window, holding a straggly rope of woven grass. The ancient highwaywoman is a pitiful sight, barefoot and in rags, with spindly white plaits to her waist. We give her some coins and drive on, grateful that her grandsons haven't joined her with guns.

By the time we head south again (towards Chile), we have got the hang of driving in Ecuador, and we hoot cheerfully when buses suddenly brake to pick up passengers, or when brightly-painted lorries hog the middle of the road, religious mottoes emblazoned across their windscreens. We pass teams of Indians working on the highway, filling potholes and digging roadside ditches with spades. The verge is dotted with shrines. Occasionally we reach a toll gate, and pay a dollar to drive along a stretch of cambered tarmac. Sometimes we crawl through litter-strewn strips of tarpaulin-covered shacks, cluttered workshops, bedraggled washing lines and tyre shops - vulcanisadores. Fruit is piled by the roadside - yard-long beans, green bananas, watermelons, huge citrons and tiny naranjillas; and shacks serve food cooked on open fires. In the distance, smoke rises from volcanoes.

We spend two nights at Hacienda San Agustin. Once an Inca palace, and then an Augustinian monastery, it is now a charmingly bohemian hotel with breathtaking views of the smoking peak of Cotopaxi, Ecuador's highest active volcano. Guillaume has been reading about de La Condamine's discovery, in Ecuador, that the earth is fatter on the equator than from pole to pole, and he's excited to learn that the famous mathematician stayed at this very hacienda in 1736.

Nearby Saquisilí market is an astonishing kaleidoscope of colour. Cotopaxi women are short and stout in gathered skirts, nylon tee-shirts with English slogans and patterned knee-socks, all in many clashing colours. We wander among stalls selling live guinea pigs, rabbits and chickens. Whole pigs roast on spits, and locals tuck into bowls of watery soup, with floating blobs of pork fat and skin.

The next town, Ambato, is described in our itinerary as "the city of flowers and fruit", but acres of building sites, rubble and litter greet us. "Drive up and down the hills always straight and you are out of the village", the notes promise. In vain, we circle dozens of roundabouts, each half-built but already embellished with a huge, scantily-clad statue. Stopping for lunch, we order cuy, a local speciality. Alas, a roast guinea pig arrives, whole and undisguised - with legs splayed, glassy eyes staring, teeth bared, and mouth gaping in alarm. Its expression matches my own, as I remember my childhood pets, and suddenly I am no longer hungry. But Guillaume tucks in, sucking the bones and spooning out the brains.

After triggering the car alarm many times, we escape the concrete sprawl of Ambato, and drive on through craggy wilderness - a pallet of ochre, olive and grey, dappled with sunshine - with tiny fields on almost vertical slopes, backed by rugged peaks and smoking craters. This is one of the poorest regions of Ecuador, and we see barefoot boys ploughing with oxen, laundry drying on bushes, and dilapidated shacks with rainbow-painted corrugated iron roofs. The local hats change from dark felt to white solar topees, which unmarried girls wear with two pompoms dangling from the crown.

We end our drive at Mansion Alcazar, a luxurious colonial house in Cuenca, in a cobbled street lined with Moorish balconies, latticed windows and overhanging roofs. In sunshine and showers, we explore gilded churches and flower markets, listen to Andean music in the square, and buy local palm-fibre hats from a workshop - for panamas, long favoured by Europeans, come from Cuenca, not from Panama.

On our last day, we drive through swirling fog and rain to Cajas, an eerie region of 200 lakes surrounded by bog, spongy moss and gushing rivulets. Walking makes us out of breath at this altitude - 12,000 feet. Knobbly yellowish crags loom into view through gaps in the mist. Gemlike orchids poke through the grey scree. This is the most dramatic of all the scenery we have seen.

Guillaume remembers that Stendhal became dizzy from a surfeit of beauty. The pot-holed Panamericana has led us through landscapes of such magnificence that we have succumbed to Stendhal's Syndrome - we are giddy with the wildness, grandeur and spectacular beauty of this extraordinary avenue of volcanoes.

First published by the Telegraph
©SarahShuckburgh