The Great Wall of China, a UNESCO World Heritage Site, is a perennial favorite among tourists and with very good reason. As an attraction it is beautiful, awe-inspiring, daunting and exciting. The Great Wall, stretching 4,000 miles (6,350km), was built in stages from the 7th century BC onwards, snaking its way across the mountains and valleys of five provinces in northern China as a mammoth defence bulwark against the neighbouring Manchurian and Mongolian peoples. Several sections of the wall, which has become the most prominent symbol of Chinese civilisation, can be viewed in the Beijing area. In Yanqing county in northwest Beijing is the 600-year-old Badaling Fortification, representative of the Ming dynasty sections of the Great Wall. Other sections can be seen at Jinshanling, Mutianyu and Simatai. The popular sections can be very crowded but generally if you walk a little way you can escape the worst of the press. There are some great stretches of the wall to hike, like the roughly six mile (10 km) section between Jinshaling and Simatai, but be careful about setting off alone as parts of the wall are unstable and unsafe. It is best to take your own water and snacks, and to pack very warm clothes if you go in winter, because the wall can be freezing. There are vendors but their goods are very expensive.