Echo Wall The Echo Wall encloses the Imperial Vault of Heaven. Its perimeter is 193 meters (633 feet). The wall is flat and smooth, which allows sound waves passing smoothly. If you and your friend stand by the wall behind the East Annex Hall and the West Annex Hall respectively and you whisper a word, then your friend will hear clearly what you said. The phenomenon utilizes the theory of sound waves, resulting in a "mysterious atmosphere". Three Echo Stone Three Echo Stones refers to the three stones from north to south on the stone road outside the gate of the Imperial Vault of Heaven. If you speak facing the vault while standing on the first stone, you will hear one echo; standing on the second and then the third stone, you will hear two and three echoes respectively.

Heaven Heart Stone, also known as Sun Stone, is one of most distinct, design-wise, in the Temple of Heaven. It is a round stone in the center of the altar which is slightly protruding. If you stand on it and shout or knock, the sound waves will be clearly echoed. In ancient times, at the Worshipping Heaven Ceremony, the ritual officer would stand on the stone to read the oration and the clangorous sound seemed to be reaching to heaven.