China Tibet, the "Roof of the World" (Bod to Tibetans, Xizang to the Chinese), has exerted a pull of almost supernatural proportions over travellers for many centuries. However, it is today a sad, subjugated colony of China. The scenery has a majesty and grandeur that are spellbinding, the religious monuments and practices are overwhelmingly picturesque and moving, and the Tibetan people are welcoming and wonderful, but this is a previously proud and independent nation in thrall to a foreign power: look just a little below the surface and it is all too apparent that Tibet's past has been tragic, its present is painful, and the future looks bleak.

This doesn't mean you should stay away, however. While tourism provides legitimacy as well as foreign currency to the Chinese government, many people, the Dalai Lama among them, believe that travellers should visit Tibet to learn all they can of the country and its people. Although the daily bureaucratic irritations for independent visitors can sometimes seem overwhelming, official Chinese policy is to increase the number of tourists, and hence tourism earnings, in Tibet. While the Chinese prefer easily controllable, high-rolling tour parties rather than the less malleable, less lucrative budget travellers, they are, for the moment, prepared to tolerate both.

The isolation of Tibet has long stirred the imagination of the West, yet until the British, under the command of Younghusband, invaded in 1904, only a trickle of bold eccentrics, adventurers and the odd missionary had succeeded in getting close to Lhasa, and then only at serious risk to their lives, for it was firm Tibetan policy to exclude all influence from the outside world. So great was the uncertainty about the geographical nature of the country even 150 years ago that the British in India despatched carefully trained spies, known as pundits, to walk the length and breadth of the country, counting their footsteps with rosaries and mapping as they went. When Younghusband's invasion force finally reached Lhasa they were, perhaps inevitably, disappointed. One journalist accompanying them wrote:

If one approached within a league of Lhasa, saw the glittering domes of the Potala and turned back without entering the precincts one might still imagine an enchanted city. It was in fact an unsanitary slum. In the pitted streets pools of rainwater and piles of refuse were everywhere: the houses were mean and filthy, the stench pervasive. Pigs and ravens competed for nameless delicacies in open sewers.

Since 1950 Tibet has become much more accessible with approaches eased by plane links with Chengdu and Kathmandu. Today's visitors are perhaps more worldly than to expect a romantic Shangri-la, but there is no doubt that many people are surprised by the heavy military and civilian Chinese presence, the modern apartments and factories alongside traditional Tibetan rural lifestyles and monasteries.

The massive Tibetan plateau , at an average height of 4500m above sea level, is guarded on all sides by towering mountain ranges: the Himalaya separates Tibet from India, Nepal and Bhutan to the south, the Karakoram from Pakistan to the west and the Kunlun from Xinjiang to the north. To the east, dividing Tibet from Sichuan and Yunnan, an extensive series of subsidiary ranges covers almost a thousand kilometres. The plateau is also birthplace to some of the greatest rivers of Asia, with the Yangzi, Mekong, Yellow and Salween rising in the east, and the Indus, Brahmaputra, Sutlej and some feeder rivers of the Ganges in the west near Mount Kailash.

Covering a massive 1.2 million square kilometres, today's Tibetan Autonomous Region (TAR) is but a shadow of the former Tibetan lands. The old area, sometimes referred to as Greater Tibet or Ethnographic Tibet, was carved up by the Chinese following their invasion in 1950, when the Amdo and Kham regions were absorbed into Qinghai, Sichuan, Gansu and Yunnan provinces. The TAR consists only of the West and Central (U-Tsang) regions of Greater Tibet and divides into four geographical areas. The northern and largest portion is the almost uninhabited Chang Tang , a rocky desert averaging 4000m altitude, where winter temperatures can fall to minus 44°C. South of this is the mountainous grazing area , land that cannot support settled agriculture, inhabited by the wide-ranging nomadic people with their herds of yaks, sheep and goats. The southern valleys , sandwiched between this nomad area and the Himalaya along the southern border, are the most hospitable for human habitation. Not surprisingly, this is the most populated area and where visitors spend the majority of their time, particularly in the extensive valley system of the Tsangpo River (Brahmaputra) and its tributaries.

There has been heavy Han migration into the region since 1950, and although it is impossible to know how many Chinese live here now, it is likely they will soon outnumber Tibetans, if they don't already. The situation is most marked in the cities, where the greatest opportunities exist: not only are the numbers of Han increasing all the time, but they are becoming economically dominant too.

It's worth bearing a few things in mind while you're here. Many of the Chinese who have come to Tibet are poor people trying to make a life for themselves and their families - they may have little knowledge or understanding of the wider political implications of their presence here. Also, life in Tibet has taken its toll on Tibetans, and there have been instances of Tibetans asking for Dalai Lama pictures or asking foreigners to take letters to relatives outside the country and then turning the foreigners in to the security forces to be deported. Be careful whom you trust, but also be aware of the harm you may be doing. Everyday conversations are going to cause no damage, but if you are seen to be asking a lot of politically loaded questions about sensitive issues then not only are you putting yourself at risk but any Tibetans who talk to you could be in danger long after you have left the country.

Tibet offers some of the most awe-inspiring scenery in the world, and the sheer scale of the high-altitude valleys, mountains and lakes in which human habitation is but a speck on the landscape is humbling. Lhasa , Shigatse and Gyantse offer the most accessible monasteries and temples - the Jokhang, Tashilunpo and the Kumbum respectively - and are also tourist-friendly cities with the biggest range of facilities in the region. The Potala Palace in Lhasa remains an enduring image of Tibet in the Western mind and should on no account be missed, and there are plenty of smaller sights in the city to keep anyone busy for several days. Farther afield, the Yarlung and Chongye valleys to the southeast boast temples and ancient monuments, and the ancient walled monastery of Samye is easily combined with these. The tourist corridor between Zhangmu on the Nepalese border and Lhasa is relatively well-trodden these days, although by no means overcrowded, and offers side-trips to the huge Mongolian-style monastery at Sakya and to Everest Base Camp .