Mechanics of the Underground
The Underground consists of the capital city, Elpidia, and 8 major cities. There are also 6 minor cities.
Each city is located in an enormous cavern ranging from 1-10 miles across. Most cities do not take up this entire space, while some (like the capital) have expanded by tunneling into the cavern walls.
The areas outside of the cities are often inhabited by wild creatures and wilder people. Not everything which exists in the caverns is good.
Each City is connected by vast tunnels hundreds of feet across and sometimes hundreds of miles long. The tunnels too can be a haven for the undesirables of the world.
Each city is completely cut off from the surface and is incredibly deep underground. The only means of getting to the surface or vice-versa is by the use of a Portal, controlled by a powerful mage, located at the very top of each city. No teleporting can enter or exit the underground (which includes summoning from another plane).
Each city is ruled by a Lord. While the Lord of Elpidia is not technically a King, he is by default more powerful than all the other Lords. The Order of the Flame carries out the orders of those Lords.
The day to day activities of each city is largely maintained by an army of mages, who are usually numerous enough to inhabit an entire area of a city, resulting in Mage’s Districts. Everthing from water to light, servants and self-drawn chariots are left to the Mages of Seara.