Beijingers talk about air pollution in the same defeated way that Romans discuss the traffic and Londoners the rain. It is choking, eye-stinging and gritty throughout the year, regardless of season.

I'm in the Chinese capital to escape the smog on a trip to the Great Wall of China, organised by Beijing Hikers, which has been arranging guided walks since 2001. My tour is fully subscribed with foreigners: some serious hikers, some Great Wall enthusiasts, but most just look like they need to get out of town for a breath of fresh air. Some talk about their time in Beijing as if it's a sentence – two months here, three months there, one old lag has lasted two years. The tour bus, meanwhile, glides through Beijing's hinterland: a heartbreaking vista of grey high-rise suburbs, bleak karaoke barns and various architectural follies that look like the victims of insurance fires.

China is beginning to open up to alternative tourism, a reaction to the country's booming domestic tourist industry which mostly resembles America's in the 1950s. There's no animal reserve without a menagerie of fibreglass tigers out front, no limestone Butterfly Cave without a 30ft concrete butterfly welded to the entrance. In a country where practically no historical monument has survived unrenovated, remote sections of the Great Wall represent a living, decaying link with China's past.