Originally built in 1420 at the same time as the Forbidden City, the Temple of Heaven was one of the four sacrificial temples of the emperors. Not only were sacrifices made to appease the heavens and to bring prosperity to the empire, but to ensure good crops in the coming year. Built according to strict religious principles, with perfect symmetry and covered in dark blue tiles representing heaven, every detail of the architecture is built in nines – the number that represented the emperor. Aside from the magnificent altars and temples, the Pavilion of Longevity and Long Corridor are well worth a visit. Here you can spend hours watching improvised performances of Peking Opera, with crowds singing Chinese songs and musicians playing the two-stringed erhu.