The smaller circular compound at top is an echo chamber enabling someone standing at the east side to whisper to someone standing at the west side. The large terraced circles below, within the walled square is where the Emporer would stand to communicate with the gods. You can, too! Stand in the very center on top of a small raised stone and your voice is amplified and mysteriously enchanced. Other echo effects take place on the various levels of the terrace. Located in central Beijing. There was supposed to be a corresponding celestial temple mirrored somewhere opposite on the feng shui grid of the city, but I can't find any trace of it.