There are many cities in China have train to Lhasa, Tibet. If time, schedule, and budget allow, we would recommend you to take train from Xining to Lhasa. Xining is the real starting point of Qinghai-Tibet Railway, all highland views starts from here. All sections before Xining are not highland area.
A 2nd railway line from Chengdu to Lhasa is underway that will wind through some of the world’s most mountainous and inhospitable territory and likely take a decade to complete. Currently the train from Chengdu to Lhasa still goes the longer route via Xining, which takes about 43hrs. The planned 2nd railway will go directly from Chengdu to Lhasa, through the mountains from Kangding in Sichuan to Nyingchi in Tibet. Once completed, the travel time will be cut from 43 to about 13 hours.
There are several overland routes to Tibet which is of particular interests to adventurous travelers. However an expedition as such is demanding in physical health, complicated in local regulations and often very costly, so unless you are determined and travel with a large gang to share the expenses, there is no need to consider it.
Should I stay overnight at the lakeside of Namtso? -- This is a questions often asked by travelers. As a local agency, we here below give you the pros & cons of staying overnight at the lakeside of Namtso, but as how to choose it exactly, it depends on what kind of traveler you are, essentially what kind of person you are.