The round Hillock was the place where emperors worshipped Heaven. It is a round platform built of blue stones. It has four tiers. The highest tier has a height of about 5 meters with a radius of 11.4 meters. It is surrounded by stone railing with 4 entrances.

The round hillock presents an interesting phenomenon. When the standing on the central round stone speaks or shouts, he will find by himself that the voice is much louder than his usual one. This is the result of sound reflection of the stone railings round the platform.