Imperial Vault of Heaven
This is the Imperial Vault of Heaven, which is a smaller structure. Seen from a distance, it looks like a blue umbrella topped by a gilded ball. This circular building has no crossbeams.  Its dome is supported by a complicated span work, which is in complete conformity with the principle of dynamics.  It was built in 1530 and rebuilt in 1752.  Since 1949 it has been renovated several times. As you can see, its decorative paintings still retain their fresh colours. After the service, the tablets of the Gods of the Sun, the Moon, etc. were placed on the stone platforms.

The Echo Wall  encircles the building by a round wall.  A mere whisper at any point close to it will send the sound travelling along the wall so that the echo can be heard clearly at the other end.  This is made possible because the wall is round, it has eaves and all the bricks are hermetically laid. In front of the steps leading down from the hall is the Triple-Sound Stones. If you stand on the first stone and call out, the sound will be echoed once; on the second stone, the sound will be heard twice; and on the third stone, the sound will he repeated three times. This phenomenon is due to the differences in the distance, which the sound waves have to travel from the stone to the Echo Wall. As a result, the sound waves returning at different intervals create different echoes.
      UNESCO listed the Temple of Heaven as one of the World Heritage sites in 1998.