Tourists visit the Mogao Grottoes in Dunhuang, northwest China's Gansu Province, Sept. 10, 2014. The largest-ever preservation project at Dunhuang's Mogao Grottoes, a collection of ancient Buddhist cave artworks, has been completed with the official opening of an affiliated visitor center on Wednesday. Occupying the caves on a 1,700-meter-long cliff, the Mogao Grottoes has some of the world's finest Buddhist frescos and sculptures, which were made as early as 1,600 years ago. It was listed as a UNESCO World Heritage Site in 1987. Since late 2008, a series of preservation efforts have taken place at the Mogao Grottoes, including cave consolidations, redesigned tourist footways, security and sandstorm-protective facilities, as well as the newly-opened visitor center, which shows digital images of the caves. Starting from Sept. 11, visitors are required to undergo an online reservation process in order to visit the Mogao Grottoes. (Xinhua/Chen Bin)