AN hour and a half's drive into the Sahara, at nightfall, the first thing you notice is the silence. This is the sound of the greatest desert on earth, an expanse so large it's impossible to grasp the scale.

And it's humbling, almost frightening, the way all the sand and the sky and the light wind over the dunes swallow up the slightest noise. But it's unforgettable.

There are many reasons to visit Tunisia. The beaches are famed for their warm seas and constantly fine weather. Jerba - which claims to be the original land of the lotus eaters, where Ulysses paused on his Odyssey - is a particular favourite for those who relish sunshine by the sea.

The architecture is impressive and the colourful souks, selling jewellery, rugs and pottery, prove temptations too great to resist for many tourists in north Africa.

But the chance to take even the briefest sample of the nomadic way of life, with just a goat-hair tent between you and the starry desert sky, is one reason why it's worth ditching the usual holiday itinerary, at least for a night or two.

We made the long drive south from Jerba, crossing to the mainland by ferry, passing one ramshackle village after another by the side of the road.

Desert communities in Tunisia have developed ingenious ways of coping with the intense summer heat - like the Troglodyte houses we saw on our way southwards at Matmata.

Surrounded by stunning rocky hillsides dusted with blue and yellow spring flowers, these homes have been dug out of the earth, successive generations preferring to live in the cool underground to escape the brutal temperatures.

On our visit the resident family received us warmly, and gave us small glasses of sweet mint tea to sip in the central courtyard while we peered sheepishly into their home.

The grandmother, who has lived in the house her whole life, was grinding grain for flour, mother and daughter were cooking in the kitchen, with two sleeping and living rooms on the other side. When the family grows, and more accommodation is needed, they simply dig another room out of the hillside.

Eventually we reached the oasis town of Douz, known as the gateway to the Sahara. After winding through the lush palms we emerged abruptly into a bleached world of powdery sand. All the buildings are gone by the road side, there's just flat desert all around and barely discernible tracks left by other vehicles ahead.

Thankfully our excellent driver - never one to waste time - was familiar with the area, and his 4x4 more than up to the terrain. He picked his course through the dunes until he finally spotted some black marks on the horizon.

This was our camp at L'Oasis de Tbini, near El Faouar in the northern Sahara. A few large tents, bound together out of goat-hair blankets, branches and rope, the only marks visible anywhere in the whiteness for miles around.

Stepping from the jeep into this inhuman landscape, the silence and the space give you just a hint of the incredible loneliness that must exist here. No wonder the Bedouin camp communities were so strong for so many years in such an inhospitable environment. You would stick with your people in a place as extreme as this.

Nowadays, very few live in the traditional nomadic way. Almost everyone has left for the cities and the towns. Some families return to the desert in the spring, spending the cooler months there before the temperatures soar into the hundreds Fahrenheit, forcing them north again.

But there is still rumoured to be one tribe, unrecognised by the Tunisian or Algerian governments, that lives like this the whole year round, moving unnoticed across borders, through the most challenging conditions on earth.

After a dinner of traditional food - spicy soup, couscous, barbecued meat - we spend the evening in a more modern adaptation of the nomad's fireside way, talking and drinking date and fig liquors.

There is even some dancing round the flames - but to the thundering beat of crazy Tunisian techno booming out of the stereo in one of the 4x4s.

As the temperature drops and the fire dies down, someone finally turns the music off and a few of us decide to take a walk into the night across the glowing white dunes.

The moon is just a thin crescent through a haze of light cloud overhead.

Tramping across soft, shoe-filling sand soon turns into something of a struggle but we make it to the top of a big sand hill and look out over the darkened desert.

Not a sound stirs. Just a light breeze moves in the night. But turning our heads to the wind, there comes the faintest sounds of people, another camp, far off in the distance. It comes clearer on the breeze - voices, just two or three, singing to the beat of drums. Who are these people? What are they doing out here? Are they "the real thing"?

Our guides were adamant. It was a genuine Bedouin camp - without the tourists or the techno - about two miles away. We were lucky to encounter them.

But confirmation that people still live this way somehow made the Sahara seem even emptier - a desolate but beautiful place.

Tim Ross was a guest of the Tunisian National Tourist Office (020 7224 5561) and Tunis Air, which flies Heathrow-Tunis four times a week.

Regional connections to Heathrow by flybmi.com and British Airways.

Dunes Voyages in El Faouar and Tozeur (00 216 76 460 101 and by email to dunesvoyager@yahoo.fr) operates two night desert tours to L'Oasis de Tbini and Douz from £89 per person (two sharing a tent). Including full board and transport, desert tours are available Sept-May.

For more details on holidays in Tunisia, contact your local ABTA travel agent