Tiantan ( The Temple of Heaven)
About 2km southeast of the Forbidden City towers Tian Tan, or the Temple of Heaven, built in the Ming Dynasty, where dynastic rulers in China used to worship the heaven and to pray for harvests. The temple plus subsidiary buildings and a surrounding garden covers an area five times the size of the Forbidden City. As Chinese emperors called themselves Tianzi, or the son of heaven, they had to cede  supremacy to the heaven in terms of abiding. Temples of various kinds are scattered in Beijing. The best-known are the Temple of Heaven in the south, the Temple of Earth in the north, the Temple of Sun in the east, and the Temple of the Moon in the west. The Temple of Heaven is the grandest of them all.

Echo Wall

The circular wall surrouding the Imperial Vault of Heaven is 193.2 meters long, 3.7 meters high and 0.9 meter thick. If one speaks against the wall at one end, another can hear his voice at the other end of it.