It is behind the icon where the alter, the holy of holies, is located. This represents the closest heaven ever comes to Earth. Access to the holy of holies is strictly regulated. Once the Eucharist is blessed the priest takes it out of the alter into the nave and dispenses it to the people. This represents the priest's role as intermediate between God/Heaven and the people/Earth.
While there is still a bit more service to go after communion the micrography of the church reaches its climax here. The design of the church has successfully brought Heaven to Earth for the faithful.