In the northwestern corner of China's Hunan Province, Tianmen Mountain is known for its massive temple and its classical Chinese mountain scenery. A cable car carries passengers above the painting-like landscape to the top of the peak. A narrow cliffside path with a railing circles the summit. A newer section of the walkway was made using a glass floor. People can walk on the 3-foot-wide panes, which sit nearly 5,000 feet above sea level, but they have to wear cloth slippers so they do not leave scuff marks. This is because the walkway is in such a precarious position that cleaning it is nearly impossible.