The Hall of Audiences was a large, unfurnished room where Landru spoke to his lawgivers and priests. It was located in the same building as the maximum security establishment and the absorption chambers.
The room in a sense represented the essence of Landru; even Marplon, a member of the underground, hesitated to open it and grant access to Kirk and Spock. Landru's projected image appeared in front of the large wall that can be seen in the image. What was left of Landru, a sophisticated computer that ran the entire planet, was located behind this wall; Kirk and Spock were able to expose it by destroying a portion of the wall, before Landru neutralized their weapons. (TOS: "The Return of the Archons")