China's rail network is the largest on earth, and a handful of its routes pay back the cost of a ticket in scenery alone. These are the five I'd pick if you want your transit to feel like part of the trip.
Xining to Lhasa — the Qinghai–Tibet railway
The world's highest railway crosses 5,072m at the Tanggula Pass. Cabins are pressurised, oxygen is piped in through vents, and the views — Tibetan antelope on the Hoh Xil plateau, blue salt lakes, snow peaks — are unlike any other train on earth.
Book a soft sleeper a month ahead (they sell out) and try for a departure that puts you at the pass around noon, so you aren't staring at a dark window for the best bit.
Guilin to Kunming — karst to red earth
The high-speed D-train through Guangxi and Guizhou runs past endless limestone pinnacles for the first three hours, then rolls onto the Yunnan plateau with its red earth and terraced fields. A six-hour ride that feels like a geography lesson.
Sit on the left-hand side leaving Guilin for the karst views; switch sides somewhere around Xingyi for the plateau.
Chengdu to Kangding — the Sichuan–Tibet highway, by rail
The new Sichuan–Tibet railway is opening in stages. The Chengdu–Kangding segment already runs through Erlang Mountain tunnels and across high bridges above the Dadu River gorge. At 4,500m elevation on the approach, you'll see prayer flags fluttering past the window.
This is a three-hour ride that replaces what used to be a punishing eight-hour drive, but the views are still dramatic enough that you won't want to nap through it.
Harbin to Mudanjiang — ice and forest
In January and February, this short (~3hr) route through frozen birch forest and across the Mudan river is one of the quieter pleasures of a winter trip. Steam locomotives still run as tourist rides near Jiamusi if you want to romance it.
Lanzhou to Urumqi — the Hexi Corridor
The high-speed line retraces the Silk Road through the desert of Gansu and into Xinjiang. You pass the snow-capped Qilian range on one side and the Gobi on the other for hours. Overnight sleepers also run on the parallel conventional line — slower, and more atmospheric.
The takeaway
Buy seats on 12306 at least a week ahead for scenic routes, and pick your side of the train deliberately — it's the difference between watching snow peaks and watching a concrete wall.