Demon Lord Council Chambers
As stated in the title, here are the chambers where the Demon Lords come to meet with one another for council meetings to decide what's happening with their race. They will discuss anything from battle tactics to concerns of the general public and all Demon Lords represent their people and themselves.
The chambers are within the city, however, their chambers are guarded well and the chamber house is prepared to be a last defense should the city actually be breached. It has many rations that could feed the entire city as well as weapons for all who would use them. It is made from the same source that the fortress is so it is a miniature stronghold in which the entire city could take refuge.
Each Demon Lord also has their own room in these chambers so long as they are of the council and are deemed fit to be on the council.
