Get in Tibet by Plane
You can fly to Lhasa and also Nyingchi but flying in from a much lower altitude city puts you at high risk of altitude sickness because of the quick transition. If you are in Sichuan or nearby (and aren't satisfied visiting the many ethnically Tibetan areas to the east of the Tibetan Autonomous Region) flying from Chengdu is the easiest option.
Interested in a Tibet tour? Browse our Top Tibet Tours!
A flight from Chengdu to Lhasa plus all the necessary paperwork will cost around 2000 yuan, and can be arranged through most large hostels or travel agents.
An alternate route is to follow the Yunnan tourist trail to Zhongdian and fly from there to Lhasa. If you spend a few days each in Kunming (2000 m), Dali (2400 m), Lijiang and Zhongdian (3200 m) to acclimatise, you should be able to fly to Lhasa (3650 m) with little risk,
Get in Tibet by Train
The Qinghai-Tibet (Qingzang) Railway from Golmud to Lhasa started operating in July 2006. The journey all the way from Beijing takes just under 48 hours, costing 389 yuan in the cheapest hard seat class and 1262 yuan for a soft sleeper. Direct trains to Lhasa originate in Beijing, Xining, Lanzhou, Shanghai, Guangzhou, Chongqing and Chengdu. For a mid-range sleeper from Chengdu with 6 bunks in each room, they are 692 yuan. Be warned that these trains are not for the faint-hearted and the less adventurous type: they do not have Western-styled toilets and bunks are relatively cramped. The main advantage for this mode of transportation is the fact that you could slowly adapt to high altitude conditions instead of a sudden shift if you were to take a plane.
If you're not up to rubbing shoulders with the hoi polloi, Tangula runs roughly weekly luxury trains (Apr-Dec only) from Beijing to Lhasa and back. The 4-day journey costs US$5,500 (twin sharing), including all meals, drinks and excursions. However, as of January 2010, the Tangula still has no official launch date and are not accepting reservations until Summer 2011, due to economic hardships.
Get in Tibet by Road
There are four roads into Tibet, roughly corresponding to the cardinal directions:
(If you are caught by the authorities you will either be sent back (at your expense), have your visa canceled or sent home or in extreme cases banned from ever re-entering China. There are even reports of foreigners being jailed on a temporary basis for breaking travel bans). Keep this in mind!
North: The road from Golmud (Geermu) is the easiest legal land route at present. The landscape is beautiful but difficult to appreciate after the long rough ride.
It's possible to travel this way by hitch-hiking on trucks if you are well prepared (camping equipment, food and water for a day). Expect to spend a few days. There are police checkpoints on the way but the only one that is a problem is the one 30 km or so out of Golmud. If you walk around it and a few km beyond you should be able to get a ride without too much of a problem. There are plenty of places to eat on the way but be prepared to get stuck in the middle of nowhere. There are also are places to sleep ranging from truck stop brothels to comfortable hotels, however these should be avoided as you're likely to get picked up by the police.
East: There is no legal way to travel this road (except as part of an expensive organised tour; see Overland to Tibet) and the security is tighter than from the north. Travellers do get through this way, but for people who are obviously not northeast Asians it's difficult.
West: From Kashgar (Kashi) much of the way is technically off limits. However there is a steady stream of hardy travelers coming this way, usually hitching rides on trucks. The road is totally unpaved for over a thousand kilometers with villages and water few and far between. The main advantages of this way is that it passes by Mount Kailash and through a beautiful, very remote region inhabited by nomads. You should be very well prepared to travel this way and take everything you would need for independent trekking: camping equipment suitable for freezing temperatures even in summer, a good tent and at least a few days of food (there are a few truck-stop places on the way but not always when you want them). Expect the trip to take two weeks or more. From Kashgar it's much farther to go to Lhasa via Urumqi and Golmud but the better transport (trains and good paved highways) make it no more time consuming to travel this way. There are many interesting things for the tourist to see on the way and it is worth considering traveling this way instead of via Mount Kailash.
South: From Nepal the international border makes any sort of breaking of the rules impossible, so the only option is to book a tour with a travel agent in Kathmandu. In addition, as of 2007, you need a group visa for China itself to cross the border into Tibet, so don't bother applying before you get to Kathmandu. The drive from Kathmandu to Lhasa takes five days and is very rough, but pretty.