These tunnels had not always belonged to the DIS. This place at its top level was once a cathedral that sunk beneath the ground during an earthquake. This made it hallowed ground, a very powerful symbol that caused weakness in general demons and killed the weaker ones as well as preventing ghost manifestation. After this several different organizations and buildings had been built on top of the land at various times. It was discovered in 1842 by miners caught up in the gold fever caused by the discovery of the precious metal in Placerita Canyon.
What happened to it after its initial discovery is murky. No records remain of its existence between 1843 and 1946. At this time it was again discovered during the craze to build atomic shelters after the A-bomb destroyed Hiroshima and Nagasaki. It had since 1842 been restored and expanded. Some miles below the surface the original cathedral had been restored. Whoever had occupied it was long dead. Everything abandoned. The structure had been built into several different facades of LA. At its point closest to the surface level there is an enormous chamber which is linked to the city’s waterways.
It is a chamber with four entrances each pointed in one of the cardinal directions (north, south, east, west). At the diagonals of these entranced are rivers feeding in from the pipes. In the center is an island made by the rivers. One this island a great sigil which no one was able to recognize or identify is carved into the stone, it is the one on the front page of the OOC. A bridge crosses over from each of the entrances.
When it was first discovered there was also a rudimentary residential area. The original tunnels zigzag and cross each other often leading in dead ends. After a thorough investigation in which the purpose of this area was not understood the DIS was given the space by the government. By this time a school had been built over top of it. The school was shut down under the guise of renovations as the DIS carved there HQ into the stone. The older tunnels are still made of roughly carved stone while the newer ones resemble the hallways of a parking structure.
The DIS started with a central space, an enormous area which spans three floors. The bottom is littered with desks with top of the line computers were analysts sit doing research, advising strike team members on how to kill certain things. Getting them credentials for what they need or information from local law enforcement areas. LA is the hub of DIS activity in America. The second level is air with a catwalk leading around the edges and crisscrossing in the middle connecting four doors that like the water room above are set at the cardinal direction.
The top level is a circular room attached to the ceiling. This is the Commanders office. The walls are made of glass but the floor is opaque so no one can see in from below. There is also a catwalk leading from four entrances to the Commanders office in the center.
The entire central space is spherical except for the flat bottom. On the bottom level is a great library which contains the hardcopy of every Occult volume that the DIS has in its possession. Below the library is a secret storage room that contains all the relics too dark and dangerous to have their existence common knowledge amongst the staff. On the second floor there is a state of the art medical centre which utilizes a combination of advances medical tactics and magic. Directly across from it on the other side of the main area is the morgue, self explanatory.
Built into the top level there are a vast number of residential rooms for the various agents that need to stay on campus, people they need to protect or seeking asylum. The crude residential areas constructed by the previous tenants on the bottom level have been turned into the containment areas. Places that are covered in so many sigils, seals and runes that God himself wouldn't be able to work his mojo in there.
On the same level as the residential district is a truly superb kitchen manned by a creature with blue skin and a truly impressive number of arms. He has the ability to know what type of food will improve someone’s mood by the way they smell and makes it upon their entry whether they ask or not. There is a training room/gym on the second level along with the medical center to make physical therapy easier to reach.
The DIS water room is linked through all the entrances. All entrances regardless of there location route either through the South or North entrances. The East and West ones lead to spiraling staircases that lead down into the spherical main room through all three levels. So the staircases are contained in glass tubes that are located on the 45 degree and 285 degrees inside the big spherical room. In case of emergency a specific phrase will cause the staircase steps to collapse into a disk that can be ridden up and down quickly. These stairs were part of the original design. They also extend five steps below the bottom of the room but merely stop, dead ending.This room is exactly mile in length and diameter.
If I've forgotten a facility that you think should be there tell me or if there something you need more clarity on. You're free to make up entrances to the DIS headquarters from the school. They have to be hard to access for anyone other than a DIS agent and have to route through the central chamber. Other than that I don't have a preference. I'll make the lost time from 1842 to 1946 a plot point later on.