On the North China Plain, about 300km from Beijing, lies an "open-air museum." Welcome to Zhengding! Within the town's ancient walls lies a trove of national treasures. For over 1,300 years, from the Tang to the Qing dynasties, Chinese architecture almost never stopped evolving here. Even China's legendary architect, Liang Sicheng, was amazed: "Half of China's architectural history is condensed right here."