A bridge made of glass

Before the bridge, this was gorge country that you walked through looking up. The Zhangjiajie Grand Canyon is a cleft between two mountain masses of the national forest park country in the Wulingyuan area, one of the ravines and gorges that make the World Heritage site a system of water as much as of rock — its valleys hold the streams, pools and waterfalls that run at the bottom of all of them. The scenic area built here belongs to the newer layer of Zhangjiajie tourism, developed as a destination in its own right alongside the older national park, with a crossing of the gorge as its centrepiece. That crossing was conceived from the start as an attraction rather than a transport link. Its official name is Yuntiandu, and its deck was specified as fully transparent glass — an engineering choice made, quite plainly, to draw visitors who would not otherwise come to a canyon trail. Where the pillars of Wulingyuan ask to be photographed from below, the bridge asks to be photographed from on top, with the gorge's depth reading straight through the floor. The canyon kept its older identity as walking country; the bridge simply stands above it now, and the water that cut the cleft keeps running beneath the crossing.

The numbers made the reputation: 430 metres long, six metres wide, suspended about 300 metres above the ground — when it opened it was the longest and tallest glass-bottomed bridge in the world. Haim Dotan, the Israeli architect, designed it, and the engineering is simple to state and hard to execute. Four support pillars stand on the edges of the canyon walls; between them stretches a metal frame carrying more than 120 glass panels, each panel a three-layered slab of tempered glass 5.1 centimetres thick. The deck was designed to carry 800 people at a time, and the builders did not stop at a walkway: three long swings hang from the underside of the bridge, and provision was made for a 285-metre bungee jump, which would rank as the highest in the world. The management committee claimed ten world records across the bridge's design and construction, and in 2018 the International Bridge Conference awarded it the Arthur C. Haydon prize, an honour for unusual structures. None of the records were permanent — superlatives in Chinese tourism rarely are — but for a structure whose purpose is the view straight down, the records were the point. They turned a gorge crossing into a headline before the first visitor ever stepped on the glass.

Opening day was 20 August 2016. Thirteen days later the bridge closed. The design capacity was 800 people on the deck at a time and an expected 8,000 visitors a day; the reported reality of the first fortnight was more than 80,000 a day, a figure no mountain gorge's paths, car parks or ticket queues can absorb. The authorities announced the closure as an urgency to improve and update the attraction — its car parks, its ticket-booking system, its customer service — and reopened on 30 September 2016 with logistics and safety measures adjusted for the numbers. The local reaction held pride and alarm together: the bridge put this corner of Zhangjiajie's canyon country onto international news schedules, and it equally demonstrated what the region's visitor economy does to any site that becomes famous faster than it can build infrastructure. The record books then moved on with typical speed; the title of longest glass bridge passed to a newer crossing in the Grand Canyon Scenic Area of Hebei province. What stayed in Zhangjiajie was the lesson, now built into the product: timed tickets, capped numbers, and glass kept clean enough to frighten people on purpose, which is, after all, the service being sold.