This article or section contains major spoilers for the plot of Blood is Mine Chapter 4: Doors and onward. New readers are advised to proceed with caution.
The Bunker is an abandoned Zone Fifty installation that currently serves as the home base of Jane Doe and her group. It is accessed through a door that seemingly leads nowhere and currently stands in the ruins of what was once a building in the Middle Tiers. Its existence was revealed to the group following Jane's first meeting with Jury S. When asked if she knew of a place where the group could set up a more permanent base of operations following Dr. Finch's home being compromised by Gesenai Shirai and Arvin Carpenter, Jury directed them to the door.
The technology that makes the bunker actually work is beyond the understanding of the group. The single door leads to many different bunkers through combinations of codes, card keys, and finger prints, however the door can only be connected to one bunker at a time. For example, if one left Bunker A and swiped the card key for Bunker B, anyone left in Bunker A would not be able to re-enter the city until the door was once again connected back to Bunker A by swiping the requisite card key. Through a combination of Michelle's knowledge and Fuse's skills, they were able to hack the lock and create a card key that allowed them access Bunker A. Originally, the party was only able to access one bunker, but through spoofing credentials using numbers found scattered around the first bunker, they were able to access three more. Fuse's program eventually turned up one other code, and a further keycard was gained by offering several useless keycards to the Tradesmen via their upgrading ritual.
According to information received from the Tradesmen, there are nineteen Zone Fifty bunkers that have yet to be discovered by the group. Of those, there are eight that are accessible by normal means and intact, one facility outside the solar system with no entrance on Earth, one facility in another time period with no entrance in the present, two facilities that are no longer present and have no entrances in this dimension, and seven facilities that have been destroyed entirely. There is no known master list of the bunkers, likely due to Zone Fifty's compartmentalization of information.
The party has access to six different bunkers.
Bunker A is the first bunker that the party was able to access. It is their main base of operations. It consists of four rooms. The door opens into a small hallway with doors leading into two other rooms. Also in the hallway is a refrigerator that was brought from Jane's house.
Through the left door is a sleeping area that has six bunks, a laundry machine, and a foot locker, as well as a small table with a microwave on it. Through the right door is a larger lab area where Dr. Finch spends most of his time. Jane's computer is also set up on one of the counters in this room, and Mom's Red has an extension growing on the large empty wall. To the far right side of the lab is another door that leads to a full bathroom, complete with a shower.
Within this bunker, Jane was able to find a series of numbers hidden in various places, namely a pair of coveralls, the inside of a cabinet, and inside the toilet tank. These numbers were what allowed the group to access the other three bunkers. When the door is disconnected from the city and opened, heavy snow obstructs any view of what might be outside. According to GPS, this bunker is on the opposite side of the world from the city.
Bunker B, also known as Zone Fifty Site Seventeen, is the second bunker that the party gained access to. It is a cryostorage facility that houses what are assumed to be failed Zone Fifty experiments. The experiments are kept in cryostasis tubes of varying sizes. This bunker consists of several rooms. The first room upon entering the door is a small room containing one cryostasis container with a door leading out into the rest of the bunker. Despite the frigid nature of the bunker and the fact that the creatures in the stasis containers are frozen, they give off a decent amount of heat. Through the door is a longer hallway containing six more cryostasis tubes, as well as two more doors. The furthest door contains a ladder leading down further into the storage facility. The other door leads into a work room that seems to serve as a base for the Proto-Juries, android workers tasked with the upkeep of Site Seventeen.
Down the ladder in the last room is a larger storage area with three large tanks. These tanks contain what are assumed to be parts of Harold Lasker, or, more accurately, parts of what Harold Lasker turned into following the Lasker Incident. Through the glass of the far back container, it is possible to see a large, grinning mouth, similar to that of Mom's Red. Another container to the right of this one contains a giant eye. No one has ventured back into this room following it's discovery, and it is assumed that no one really wants to.
The door when discontented leads to a crate formally storied in a warehouse. Jury S was rebuilt here.
Bunker C is by far the strangest of the four bunkers. The door opens onto a small platform above a dark, deep pit. There is a ceiling above the platform, which is a drop ceiling with movable tiles. This ceiling, however, is also the floor of the bunker. If an object is dropped by someone standing on the platform, it will hit the floor and make a noise that sounds a though it is coming from the ceiling. This is because Bunker C, in actuality, is an infinite loop or mobius strip. If one of the ceiling panels is moved aside, it becomes possible to drop an item and have it cycling through the room for potentially eternity. It has been shown that air resistance will eventually cause the item to rotate, but if left uninterrupted, it will cycle past the platform approximately once every twenty seconds.
Things do not get any less strange when the door is disconnected from the city. Attempting to open the door from the inside while the door is disconnected is impossible, as it is blocked by something so large and heavy that even Michelle could not budge it. Also, something on the other side of the door is capable of speech by repeating back words it has heard, almost like a recording that has been pieced together from bits of sentences. By the time Michelle left, it had begun to imitate laughter in a very unsettling manner by stuttering vowel sounds.
Dr. Finch hates this room due to it's impossible nature and dislikes being in it for even a short period of time.
Bunker D is located on Mars. It is likely the remnants of Zone Fifty's exploration of the planet, and has been left undisturbed for around 100 years. It is the largest of the accessible bunkers and has the most amenities, however the group is hesitant to make this their base as the building is very old and there is no telling how long it will continue to hold up. It consists of an entrance hall, two sleeping areas, a mess hall with a stove, an office, a full bathroom, and a medical lab. There is also a large airlock that opens up on to the surface of the planet.
The most striking thing about Bunker D is that it houses many plant containment units that have overgrown over time, some of them breaking and flooding the bunker with yellow daisies. These containment units are a key part of the oxygen generator that keeps the atmosphere inside the Mars bunker breathable. There is a control panel in the main hall of containment units that allows the pods to be set to grow any number of plants. Dr. Finch suggests that the yellow daisies that currently overrun the place are the system's default setting.
Inside the office, there is a computer terminal that still functions. Fuse was able to hack into it and have a look at the files it contained, which included old emails between Zone Fifty personnel and a manifest of soil and rock samples that were being sent from the Mars base back to another part of Zone Fifty responsible for analyzing the samples. It is safe to assume that their mining operation eventually led to the discovery of the blood on Mars.
Among the other amenities available on the Mars base, there is also a very old bio-printer. It is still functional, but occasionally jams and runs across other problems. It is assumed that this bio-printer is a very early prototype from before the technology was mostly perfected. Currently, it is loaded with biopaste and is ready to be used.
When the door is disconnected from the city, it leads to a small room that contains a ladder going down. At the bottom of the ladder is a small hallway with two doors. One door leads to a small room with an electrical panel that originally had very badly frayed wires, but has since been repaired. The other room is an office was previously overrun by a large, viney plant that was attached to the remains of a scientist known as Dr. Deaglan Camp. Dr. Camp's remains and those of the plant have since been removed, freeing the office up.
Bunker E is the only bunker that has been found that also possesses a card reader door. The outside door of Bunker E can be used to access other bunkers as well as Bunker E. Bunker E itself is the remains of Zone Fifty's experiments on a trio of ghost children they named Edison, Faraday, and Tesla. It consists of a main entryway with a door that advises that no electronics should be taken beyond it. Inside the bunker proper are several large Folkat -- or Folded Katana -- Generators skimming energy from their surroundings and using it to power the entire bunker system, as well as pieces of research and containment units for the research subjects. Currently, all of the original three subjects "live" in the bunker. Tesla has free reign of the place, but mostly stays in a small side room with a repaired television screen previously used to communicate with Faraday, the other resident. Faraday was once spread throughout the bunker following an experiment that was performed on her, however following Mine's reproduction of incident F, she is back to normal. This bunker also contains a number of "imprints" (ghosts) that Faraday originally triggered to help Jane and co. find out what happened to her, and to help them help Tesla.
The outside door of Bunker E is located in an abandoned town called Ilworth, which is in what is assumed to be the in-universe equivalent of the United Kingdom. It is a twenty-minute drive from a populated city called Southden.
Bunkers F and G
As of comic 1157, the computer program Fuse set up to locate new bunkers has found two new ones, tentatively named Bunker F and Bunker G. They currently remain unexplored.
Bunker X, or Zone Fifty Site Twenty Four, is a challenge-style dungeon like one found in a video game, which has presumably been created by the Tradesmen to allow cosmic entities that wish to help -- or hinder -- Jane and co. offer challenges with rewards that will make their fight against Thale easier. There is nothing housed in Bunker X that is required for them to be able to take down Thale, and it is offered more as a diversion with the promise of fabulous prizes. The Tradesmen have revealed that it functions much like a video game, albeit with real consequences. A party may enter a floor whenever they choose, but may only leave once they finish the floor. The challenges are predetermined, and do not change based on party configuration. Party members may be added or removed between each floor, and the elevator used to travel between floors will always take the party to the next floor they have yet to beat. Death is a very real consequence, and it had been advised to not take the idea of the challenges lightly.
In Comic 1157 - Go see the worm, Caius opens the bunker door, revealing tall grass reaching at least 8-10 feet in height which is home to at least one large mutated rabbit.
Fuse described it as "an optional hard-mode dungeon".
Floor 0 was started on comic 996 has been completed as of comic 1018. The style of the floor is very similar to that of the The Hospital, having similar enemies. However the Tradesmen made the floor harder than The Hospital actually was, by adding cybernetics, acid, and poison to the enemies. The rewards from the floor were a few pages with information on how new and old magic differs, and a breakdown of a ritual to summon bone armor.