The convoy of 4x4s was clearly silhouetted against the setting sun as it trailed along a ridge. We watched it as it suddenly disappeared over the top. We had stumbled by chance on the Friday session of "dune-bashing", a weekly treat for the hundreds of thrill-seeking Omanis who gather beside a lonely sand dune in the Omani capital's Bausher district to watch a group of daredevils hurl their vehicle down the near-vertical drop.

In Arabic they call it tloua al ramel, or "climbing the sands". The fearless drivers attack the gradient forwards or backwards, but sometimes fail to reach the top as their engines scream and sand gushes out from the wheels. Those who turn tail halfway up the towering dune are jeered by the crowds below. But when a vehicle reaches the summit and turns around, it comes down at terrifying speed. On that Friday afternoon, our elderly driver Saif winced at the sight, while the youths - all male - at the foot of the dune cheered.
You won't get far without a 4x4 in Oman. This Gulf state with a colourful history was thrust into the modern age by its Sultan when he deposed his father almost 40 years ago. (The bloodless coup was described euphemistically by one Omani official as "a family affair".) But watching that dune-bashing spectacle had made me nervous about my desert tour.

Nevertheless, two days later I found myself climbing into a 4x4 to explore the dunes of the vast Wahiba sands. The first thing I did as we set off was to ask our guide, a young French woman called Emilie, whether she had ever turned her car over. I was reassured by her response. After a three-hour drive from Muscat, with the modern road chiselling through the jagged Hajar mountains or running alongside the wadi (a channel that's dry except in the rainy season), the Tarmac suddenly came to an end in a dusty village. We were entering the realm of the Bedouin.

After a quick pit stop, when the tyres were let down for better handling in the sand, we were barrelling along at 60km/h - skimming gently on a sandy track as Emilie explained that it's like driving on ice. You might expect to speed through the immense desert wastes in silence. But Emilie preferred to listen to the strains of the Gotan Project's La Revancha del Tango as she drove through long valleys dotted with clumps of grass, where endless chains of golden and reddish dunes - nicknamed the "strawberry" dunes - rose to about 200m on either side.

There was not a soul in sight, and there were just two reminders that modern life occasionally intrudes on the desert: the occasional blue signpost pointing to a camp where tourists could spend a night under the stars, and sporadic bags of rubbish or plastic bottles left behind by visitors.

Lunch was a picnic of salad and date biscuits under an acacia tree at the foot of a dune. I walked to the top, my feet sinking into the soft sand. Here I could see the tracks of camels and scarabs, contemplate the majestic sweep of the dunes - and try to banish the thought that I might be bitten by a scorpion. The silence was broken only by the flies buzzing round my head and the occasional hum of a jet overhead; Oman lies beneath some of the planet's busiest aviation highways.

Three-quarters of the territory of Oman is desert. Our visit to Wahiba was a foretaste of the Empty Quarter, the huge desert straddling the border with Saudi Arabia that is memorably described by the British adventurer Wilfred Thesiger in his book Arabian Sands - a must-read for any visitor to Oman. I learnt in the book that Thesiger was not the first to cross the Empty Quarter. Around 1930, the Englishman Bertram Thomas walked across from south to north.

 few months later, his compatriot St John Philby - the eccentric father of double-agent Kim Philby - took camels in the opposite direction. Philby decided that he liked life so much in Saudi Arabia that he stayed in Riyadh, converted to Islam and became known as Abdullah.

Thesiger explored just 15 years later. Like Thesiger, we were offered coffee and dates by a Bedouin family. These days, they make a living from camels and selling handicrafts to tourists. Most of Oman's 10 000 nomads are now settled in camps or villages, although the fishermen spend weeks away on fishing trips.

Welcoming us to his makeshift home, where the roof was covered with date-palm leaves, 10-year-old Mohamed showed us his biology textbook and told us, in broken English, that he is learning Arabic and English at school. Carpeted with Bedouin rugs, the little hut had a couple of chairs and a television. And, of course, a 4x4 parked outside. "Moo al akhbar?" ("What's the news?") is still the first thing an Omani villager asks a visitor. It is the greeting of the Bedouin since time immemorial.

Throughout its history, Oman has been convulsed by tribal warfare. The fabled land of Sinbad the Sailor, Oman was long a seafaring power. In the 19th century, it ruled the waves from East Africa to India. Omani wealth also came from the lucrative export of frankincense, the aromatic gum from a tree found in southern Oman. It forms the base of the heady perfume Amouage, branded as "the most valuable perfume in the world".

The dark skin of many Omanis, whose country was once a major slave-trading nation, reflects inter-marriage from the days when Omani control extended down the Indian Ocean as far south as Mombasa and Zanzibar. But India has also left its mark in the delicate architecture of the Muscat district of Mutrah, where Indians run the gold market in the souk and sell pashminas in the stores.u o Slavery ended officially only in 1970, after the Sandhurst-educated Qaboos overthrew his reactionary father, Sayid Said bin Timur, in his palace at Salalah with the covert help of the British.

Oman's mountains provide the strongest lure to visitors. The giant slabs that dominate practically the length of the country were created hundreds of millions of years ago by the collision of Arabian and Asian tectonic plates. Glinting in the sunlight, they look like poured liquid.

Your first close-up view of these russet-coloured serrated peaks is likely to be on the well-travelled road from Muscat to the fort town of Nizwa. The local craftsmen produce elegant silver jewellery, and the Friday goat market is another attraction. Oman has 500 forts, but the ancient Nizwa fortress has been well restored and, tucked beside a palm grove and surrounded by mountains, it overlooks the town.

On the road to Nizwa there is a turn-off to the Jabal al Akhdar range and the mountain pass, which climbs to 2 020m. Once again, a 4x4 is essential, in fact, mandatory, to access the region, once closed for military purposes. A soldier still waves the traffic through a checkpoint at the entrance to the mountain road. But here is the great surprise: instead of a white-knuckle ride along a winding track, a smooth road almost as wide as a motorway eases its way to the top. That said, it still took half an hour to reach the summit, after which the road gradually descended to a plateau where the only hotel is located.

Jabal al Akhdar means "green mountain", and the reason for the name soon becomes clear: the plateau is the market garden of Oman, growing peaches, pomegranates and apples on terraces that cling to vertiginous mountain cliffs. The Sultan owns a farm in the upper reaches, where donkeys trek through isolated villages that offer wonderful views of the sunset.

At this time of year, if the temperature is 25C in Muscat, you can be sure it is freezing in the Jabal al Akhdar. The night we stayed at the Indian-run hotel, there was a howling gale. The next morning I needed my coat and scarf in the biting wind, while our guide, Shakir, wore a winter-weight head cloth and thermals under his fetching peach-coloured dishdasha, or long robe. I followed Shakir into a valley of almond trees. While he leapt from stone to stone like a mountain goat, he pointed out the mauve Oman SAS markings, to guide soldiers on training missions. We explored an abandoned mud-brick village, one of the many you see around Oman.

The Sultan has encouraged people to move to larger, less isolated communities so that they can have improved access to water and electricity, health care and education. Every modern house, some palatial, has a water tank and satellite dish on the roof. In the lower reaches of the Saiq plateau, rich in fossils and studded with juniper trees, there's a spot called Diana's Point, where Prince Charles camped with his then-wife during one of his frequent visits to Oman.

The Jabal al Akhdar is home to what has become known as Oman's Grand Canyon. The views are as breathtaking as in Arizona, but in the mountains of Oman you are almost completely alone. There is no viewing platform and no visitor centre (though a new hotel overlooking a precipitous drop is a year from completion. From the Saiq plateau, the mountain range soars upwards to the country's highest peak, the Jabal Shams, at over 3 000m, its summit dusted with snow at this time of year.

It was time to drive the 150km back to the comforts of Muscat and the warm waters of the Indian Ocean. As well as having the most spectacular desert and mountain scenery, the Sultanate boasts some of the best beaches in the world. For Omanis, however, beaches serve as impromptu football pitches. Every Saturday afternoon, the long stretches of sand that run from the InterContinental Hotel are filled with back-to-back football games.

We stopped en route at the village of Fanja, situated in a date grove along a wadi. At this time of year, the wadis are dry, but in the spring they can suddenly fill with a vengeance. In Fanja, the modern village is overlooked by the ruined turret of a fort and the mud-brick homes abandoned when villagers relocated down the hill to take advantage of the amenities. We walked up to the fort. Two grizzled old men emerged through the village gate and slowly made their way to a ramshackle house, which, amazingly, had a satellite dish on its roof. "What's the news?" they asked Shakir and Saif. And we all laughed.