Tibet (Bod to Tibetans, Xizang to the Chinese), the "Roof of the World", has exerted a magnetic pull over travellers for centuries. 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 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. Tibet today is a sad, subjugated colony of China. While foreign visitors are perhaps more worldly than to expect a romantic Shangri-la, there is no doubt that many are surprised by the heavy military and civilian Chinese presence, the modern apartments and factories alongside traditional Tibetan rural lifestyles and monasteries. All this doesn't mean you should stay away, however: though 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.

In reaching Tibet, you'll have entered one of the most isolated parts of the world. The massive Tibetan plateau, at an average height of 4500m above sea level, is guarded on all sides by towering mountain ranges: the Himalayas separate 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.

Tibet's isolation has long stirred the imagination of the West, yet until the British, under the command of Colonel 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:

Since the Chinese invasion in 1950, Tibet has become much more accessible, with approaches eased by plane links with Chengdu and Kathmandu. There has subsequently been heavy Han migration into the region, and although it is impossible to know how many Chinese live here now, it is likely that they outnumber Tibetans. 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 – a situation that will be further exacerbated by the completion, due in 2007, of the railway line from Golmud to Lhasa.

Today's Tibetan Autonomous Region (TAR), though covering a massive 1.2 million square kilometres, 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, 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 at an average altitude of 4000m, 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. Eastern Tibet, occupying around a quarter of the TAR, is heavily forested. The southern valleys, sandwiched between the nomad area and the Himalayas 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.

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.

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 – though the trip is likely to be expensive, as the Chinese authorities are keen to milk tourism by charging for permits to enter the region and restricting accommodation and transport options available to foreigners. Tibetan organizations abroad ask that visitors try, wherever possible, to buy from Tibetans and to hire Tibetan guides. At all times, you should avoid putting Tibetans – and yourself – at risk by bringing up politically sensitive issues; remember that you (and your emails) are monitored here. It's also advisable not to bring in Dalai Lama pictures to hand out – Tibetans found with them are in serious trouble.

Finally, remember that the situation here is not black and white. The Han Chinese in Tibet are not demons – most are poor people trying to make a life for themselves and their families, and they may have little knowledge or understanding of the wider political implications of their presence. And don't idealize the pre-Chinese Tibetan administration; it was, after all, a xenophobic religious dictatorship, feudal in outlook, which stifled economic progress and tolerated slavery.