Gansu's Dongshan tunnel at average altitude of 3,850 meters drilled through

A worker of the China Railway No.4 Engineering Group walks in the Dongshan tunnel along the national highway No. 213 in Yugur Autonomous County of Sunan of northwest China's Gansu Province, on March 2, 2021. The 3,639-meter Dongshan tunnel at an average altitude of 3,850 meters was drilled through on Tuesday. It is a critical project for national highway No. 213 that connects Sunan to Qilian County in Qinghai Province, also in northwest China. (Xinhua/Chen Bin)