Heaven Gate Cave is the defining feature of Tianmen Mountain: a natural arch approximately 130 metres high and 57 metres wide, formed in 263 AD when the rear of a cliff cave collapsed, leaving an opening that frames the sky like a window punched through solid rock. The arch is visible from the city of Zhangjiajie far below, and from the cable car during the ascent — each angle produces a completely different impression of its scale and position.
Reaching the arch requires climbing 999 steps (or using parallel escalators) from the lower section of the plateau. The staircase itself is dramatic, cutting directly up through the rock face toward the opening. Standing in the arch and looking out through the opening toward the cloud layer and the city visible far below is the mountain's best single experience. On clear days the view is extraordinary; in mist, the effect is perhaps even more powerful, with the city invisible and the arch framing only clouds.