The Qinghai-Tibet Railway is a railway line that runs from Xining, Qinghai Province in China to Lhasa, Tibet Autonomous Region. It is the world's highest railway, with the highest point being 5,072 m (16,640 ft)
From Wikipedia
The Qinghai–Tibet railway or Qingzang railway, is a high-elevation railway line in China between Xining, Qinghai Province, and Lhasa, Tibet. With over 960 km (600 mi) of track being more than 4,000 m (13,123 ft) above sea level, it is the highest railway line in the world.