Qinghai–Tibet railway

Known as the Qinghai-Tibet train, Qinghai-Tibet railway, Tibet railway or Qingzang railway, this route is 1,956 km long and stretches from Xining in the province of Qinghai via Golmud to Lhasa in Tibet. The highest railway in the world, rising up to more than 5,000 meters (16,000 ft) above sea level, the railway is a masterpiece of engineering. During its construction it was both welcomed and opposed; and according to critics it is was built for political and military rather than an economical reasons. On the one hand, the railway enables freight to get into Tibet faster, cheaper and safer than the old highways, but on the other hand the railway obviously facilitates the movement of ethnic Han Chinese to Tibet, something opposed by many Tibetans. It also enables better control by the central government over Tibet, similar to how railways in the nineteenth century tied the nations and empires of Europe and North America together.

History

As early as 1949 when the People's Republic of China was declared and when Tibet was "peacefully liberated" in the 1950s, plans were made up for a railway to Tibet. The first section from Xining past Golmud to Nanshankou was finished in 1984, but the construction of the rest of the railway across the high plateau posed several challenges, wherefore construction was halted until 2001:

Almost 90% of the second section of the railway goes through terrain more than above the sea level. With lower air pressure and therefore less oxygen, working at this altitude was heavy for both construction workers and machinery. As diesel locomotives need oxygen to function, and there's less of it available than at sea level, trains using the line are hauled by three locomotives.
For about 550 km the tracks cross permanently frozen ground (permafrost), and if the ground were to melt from heat from the train, the tracks would be displaced. In order to keep the ground frozen, thousands of heat exchangers were jammed into the ground where the tracks were laid.
The highland is inhabited by yaks and antilopes that wander across the tracks every year in large hordes. Therefore several wilderness crossings had to be built, and for long stretches the railway goes on viaducts, which as a bonus prevents trains heating up the ground.
The final major problem was the moving sand dunes on the highland. To protect the tracks from drowning in sand, big rocks were set up as barries next to the tracks.
Construction was restarted in 2001, the railway was finished in 2005 and one year later regular traffic started. Since then, travel along this railway takes passengers to the highest point of any railway (Tanggula pass, 5,072 m), the highest railway station (Tanggula station, 5,068 m) and the highest railway tunnel (Fenghuo-Shan tunnel, 4,905 m) in the world.

While the trains have all sorts of technical adaptations to make them suitable for the extreme conditions of the route, most notably oxygen nozzles in the corridors and cabins, from a traveler's point of view trains to Tibet are largely identical to any other sleeper service in China, so don't expect a luxury service. The line is also not high speed. Line speeds average around 100 to 120 km/h, and slower on the uphill stretch between Golmud to Lhasa.
Trains usually comprise 16 cars, with a dining car located between the soft sleepers and the rest of the train. There are usually two toilets per carriage, one Western-style and one squatter; as usual in China, bring your own toilet paper. There are no showers, but there is a row of sinks for washing up. Unlimited hot water is available for instant noodles etc.
Soft sleepers are equipped with four bunks and luggage can be stored in an overhead compartment or under the lower bunks, but space is limited, so don't bring a huge suitcase.
Finally, as elsewhere in China, expect loud discussions in nighttime, smoking on board even if it's prohibited and other potentially jarring behavior. Nevertheless, you should probably just take it as a cultural experience.

Branded trains

Since 2017, several trains running on the line have been branded as Tangzhu Ancient Route (唐竺古道号 Tángzhú gǔdào hào), with special Tibetan-style decor throughout. Facilities are otherwise the same and so is the price, but it's worth trying to ride one of these if you can as they're more atmospheric than the other standard trains.
As of 2018, these operate on the Xining-Lhasa-Xigaze route (train Z6811/2) and for trains between Lhasa and Xigaze (Z8801/8802/8803/8804).

There are direct trains from Beijing, Chengdu, Chongqing, Shanghai, Guangzhou, Lanzhou and Xining to Lhasa, although not all of these operate ever day. All services converge at Xining, which is the actual starting point of the line, and thus has a total of up to 5 trains per day in high season. Many travellers opt to fly or take another train into Xining and start their journey there, instead of doing the full two-day haul from Beijing or Shanghai.
There are three classes on the train: hard seat, hard sleeper and soft sleeper; see China#Classes for a description of these. Here are some sample prices for tickets as of 2017:

Travel time
Xining-Lhasa
Lanzhou-Lhasa
Beijing-Lhasa

Tickets for the lower beds are slightly more expensive than upper beds; for example going from Lanzhou to Lhasa, a ticket for a lower bed costs ¥854 when the price is ¥823 for the upper bed.
In the summer peak season, demand for tickets far outstrips supply and obtaining them yourself can be difficult to impossible, particularly if you're aiming for soft sleeper class and/or want to have your entire group in the same cabin. Most visitors opt to let their tour agency do the legwork, which may include dealing with the grey market and paying a multiple of the official ticket price. It's often easier to find seat *from* Lhasa than to Lhasa.

These things you will want to bring for the trip:

• Enough toilet paper — as usual in China, you can't count on any being available in the toilets.
• Food — the food in the dining car is adequate, but not a memorable culinary experience. There are also carts running up and down the aisles selling mildly overpriced snacks, lukewarm beer and fresh fruit. It's better to do like most locals and bring some instant soup or noodles and heat up them with water from the hot water fountain. Moreover, in a high-altitude environment it's important to drink a lot of water.
• GPS and altitude tracking - unsurprisingly mobile phone coverage en route is spotty at best, so download an app that can work fully offline if you want to follow your progress.
• Any medication you need, including medication against altitude sickness.
• Bedding is included only in the soft sleeper class, in other classes you need to bring your own.

Almost all foreigners need a visa to visit China and to travel to Tibet by train (or other mode of transportation), you need a Tibet travel permit on top of that. Also, due to the high altitude of the train route and Lhasa itself, you should stay at some intermediate destination for a few days to let your body acclimatize — for instance at Xining, which is about 2,300m above the sea level.
There are trains from several places in China to Lhasa, and as the Qinghai-Tibet railway is the only one into Tibet, you will travel along it from Xining to Lhasa, no matter if you start in Beijing, Xining, Lanzhou, Shanghai, Guangzhou, Chongqing, Chengdu or somewhere along the way. See details in these city articles for getting in. You could also reach Golmud via routes described in Silk Road and Along the Yellow river. Some trains go daily, others every second day — on average there are five passenger trains a day in each direction on this railway.
If you plan to travel in the other direction, see Lhasa#Get in for getting to Lhasa and starting the train journey from there. Most likely you will fly into Lhasa.

At the end of each car there is a display showing the current time, the speed, the altitude and the next station. There are also posters about the route and the station (and how long the train stops there). At the stations it's allowed to go out on the platforms, but as per the schedule, other than in Golmud the train only stops for a couple of minutes. Formerly the trains also stopped at dedicated viewpoint stations on the high plateau, but this practice has ended as people frequently passed out due to the lack of oxygen.
The best views are to be had between the Tanggula Pass and Lhasa. Stations and things you can see from the train include:

• —
• —
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• , the east part of Kunlun Mountains (Hoh Xil Mountains to Bayan Har Mountains), Yuzhu Peak and its glacier
• , Tanggula Mountains. Located in the Tanggula Pass.
• — - apparently only trains starting and terminating in Xining stop here
• —
• —

While this is a normal passenger route, travel along this railway can be considered more of an aventure and the journey
cannot be recommended to everyone. You will experience conditions that otherwise only mountaineers will experience — there are likely no higher place in the world that you can reach by scheduled land transport, the train will go higher than any summit in Western Europe or the lower 48 states and unlike airplane cabins the train cars are not pressurized.
The journey should not be taken by persons who have any heart-, lung-, blood circulation-, or kidney-related health issues. The trip can also not be recommended to children and people who are afraid of wide spaces or heights or easily get panic attacks.
There will be medical staff onboard between Golmud and Lhasa and supplemental oxygen will be pumped into the cars when you travel 3,000 m above sea level or higher. If that is not enough, you can plug a nasal catheter into an outlet for a more concentrated dose. Few passengers require these, but they are available if you do.
During the journey (and in Lhasa), drink a lot of water to avoid dehydration, but no alcohol or coffee. Sunburn on the train is unlikely, since the windows are UV-shielded, and stops at stations are few and far between and usually last under 10 minutes.

Tibet is still a "sensitive" region and under military control. Being caught possessing politically hostile literature or weapons or photographing military or police will get you into trouble.
When arriving at Lhasa railway station, be prepared to be greeted by armed soldiers and police officers, ushering people off the train and the platform. IDs are checked when leaving the station, and if you show a non-Chinese passport, the guards will take you aside to a separate building to check your Tibet Travel Permit before you're allowed to leave the station and meet your guide.