Tianmen Mountain, China. Tianmen Mountain (Heaven's Gate Mountain) is a cave natural arch eroded through a karst syncline. It is located within Tianmen Mountain National Park, about 8 km south of the city of Zhangjiajie in northwestern Hunan Province.
Tianmen Mountain in is a very popular tourist attraction because of the Glass sky walk, located 4,690 feet above the sea level on the side of the Tianmen Mountain in Zhangjiajie province of China. Walking on this see-through glass is a terrifying and thrilling experience, but definitely not for the faint hearted. If you are afraid of the heights, just don't look down while walking on that Glass.