I took the train up and flight back.. and yes, the terrains are vast and amazing

lemme remind you, train from ChengDu to Lhasa is circa 36 hours, and 46 hours from Beijing, on soft (and thin) sleeper bed, passing through some of the highest terrains above 5,000m where air is even thinner than Lhasa's airport which is around 3,500m only. You may wanna think twice of train up and train down.. haha

nope, not the usual bullet train. it's the green train running tibet-tsinghai route. top speed probably at 130-150 but most of the time is around 90-120 due to ascending terrains. I measured it using waze when nothing to do in the train lol.

the best cabin you can get is soft sleeper cabin that sleeps 4. i.e. 2 double deckers. you will need to sleep with strangers, and during my time, i was with 2 very kind tibetan elder ladies and a vietnamese solo tourist.

they will switch train at xining station to change to oxygen supply train. but that being said, oxygen is not supplied automatically in the cabin. Rather, they have oxygen outlet beside your bed, similar to hospitals, and if you need any assistance, you gotta ask the staff to provide you the oxygen hose and ventilator. my SpO2 level dropped down to 60% during the most extreme cases (at kekexili plauteau and tanggula mountain range > 5,300m) with severe headache and lost of breathe but i survived lol.

view is awesome after your cross tsinghai plateau. and depending on the time of your train, you will see different view. but most of the time you will see snow capped mountain, vast grass land, countless mountain tunnel passes and occasionally wild animals.