The Qinghai-Tibet Railway, as the only railway that links Lhasa railway station to the existing rail network of mainland China, is always busy throughout the year. Because Tibet is called the roof of the world, the Qinghai- Tibet railway system is called the sky road itself. Starting from Xining City, Qinghai Province, this Tibet railroad passes through Golmud City, Kunlun Mountain Pass, and Yanhe Riverside then crosses Tanggula Pass and enters the Tibet Autonomous Region of Amdo, Nagqu, Dangxiong, Yangbajing, and Lhasa.