China has announced the completion of the first railway line to Tibet - one of the world's highest train routes.
Construction has involved several engineering feats
The pan-Himalayan line climbs 5,072m (16,640ft) above sea level and runs across Tibet's snow-covered plateau - dubbed the roof of the world.
Trains travelling on the line will have to have carriages that are sealed like aircraft to protect passengers from altitude sickness.
The line is expected to take its first passengers next year.
The official Xinhua news agency said $3bn had been spent on the challenging 1,142km (710-mile) final section, after four years in construction.
The workers who built the line had to breathe bottled oxygen in order to cope with the high altitudes.
China says the line will promote the development of impoverished Tibet.
The line links the Tibetan capital, Lhasa, with the north-western province of Qinghai.
But even before the railway line opens there are concerns about its future. The National Climate Centre said in June that rising temperatures would affect operation of the railway by 2050.