This is where all the legal decisions are made. The building itself is underground. The only part visible from the surface is an octagonal courtyard that leads the main entrance to the underground hall.
These are the underground sewers. The 4th Division is the only division that knows is well, as they use it as a supply route to get from one are to the next easily.
There are four gates which lead into Seireitei. North, South, East and West. However, they are all protected by a Gatekeeper who will not let anyone past unless defeated.