Zhangjiajie is a forest of some three thousand stone pillars in Hunan, in southern China, many of them over 200 metres tall and standing completely clear of one another. The rock is quartz sandstone, and it splits along vertical cracks. Frost, roots and running water widen them until whole slabs drop away, leaving columns where softer stone would have left caves. The shape is rare enough that geologists named the landform after this place. Among the pillars a natural arch, the Bridge Across the Sky, spans a gap high over the forest floor. Avatar's designers drew on these spires for the floating mountains of Pandora. In 2010 the park renamed its most famous one after the film, and the clifftop path at Yuanjiajie ends at a platform facing it. On a wet spring morning that begins to clear, cloud pools deep in the gaps with only the tips showing. From the terraces of Tianzi Mountain you watch the sun come over the ridge and warm the grey rock to orange one column at a time. That window lasts an hour or two.
The Bailong elevator runs up the outside of a cliff in a glass cabin, 326 metres in under two minutes. By the top you are looking down on columns you were walking between a few minutes earlier. At the edge of the park a glass bridge crosses Zhangjiajie Grand Canyon, 430 metres end to end, the valley floor 300 metres below the transparent panels. People go across it slowly, and some hold the rail the whole way. Then there is the bottom, which is a different place altogether. Down on the path along Golden Whip Stream the macaques work the trail and will help themselves to an open bag, ferns streak the wet rock, and the pillars you were looking down on an hour ago close in overhead.