Tianmen Cave 天门洞, also known as 'Heaven’s Gate' is the world’s highest cave of its kind. Located within Tianmen Mountain National Park, Zhangjiajie, in the northwestern part of Hunan Province in China.

There are 999 steep and narrow steps up to the cave which locals have dubbed as "The Stairway to Heaven".

The number "9" has some significance in Taoist tradition as it is a symbol of the emperor ('Son of Heaven'), and the supreme number that is available for a person.