(FILES) This file photo taken on August 21, 2016 shows visitors crossing the world's highest and longest glass-bottomed bridge above a valley in Zhangjiajie in China's Hunan Province on August 21, 2016. The world's longest glass bridge, over a scenic canyon in China, has been closed on September 3, less than two weeks after it opened after being overwhelmed by a swarm of visitors. / AFP PHOTO / FRED DUFOUR