Windowless Building

The Windowless Building (窓のないビル) is a tall building that is literally windowless; located in the 7th School District, it is the main base of the General Chairman of Academy City, Aleister Crowley, and the prison of Fräulein Kreutune.

Outside
As its name suggests, the Windowless building contains no windows, corridors, stairs, air ducts and no sign of a visible entryway. In the anime adaptation the building is white colored structure, several stories in height with spires and aerials jutting out of the top. During the night purplish light covers the building giving it an eerie glow compared to the surrounding buildings in the area.

The Windowless Building is located around the middle of the city, and was at the center of School District 7. It was not open to the general public and it was constantly protected by strict security. Buildings such as shopping malls and hotels were built around it. The area around the Windowless Building modifies the ley lines around it, such as the colors of the signs and lights being all uniform. And there is a presumption that not only the lights and signs were arranged, but the locations and heights of the buildings were controlled in a fashion that fully controlled the flow of people through the area, and done in a way that it would be noticed on first glance.

Inside
The only directly shown room inside the building is the quadrangular room where Aleister Crowley resides in, where several tubes and pipes cover the walls and ceilings. Despite its lack of ventilation however, the room is described as chilly.

The most notable feature of the room is the single glass cylinder with a life-support system that houses Aleister Crowley. Filled with red alkaline recovery fluid which tints the room it penetrates into his mouth and nose, causing chromatid interference in every cell, it also contains several wires and cables that are connected to Aleister's body.

Calculate Fortress
Calculate Fortress (演算型・衝撃拡散性複合素材(カリキュレイト＝フォートレス)) is the mysterious material that the Windowless Building is composed of. It is apparently strong enough to protect the building from a nuclear strike and remain unscathed, and is able to withstand, without a scratch, an attack from a concrete wall-turned projectile that Accelerator threw at it using five minutes worth of earth's rotational momentum (an entire building in the anime). This attack slowed down the planet's spin by five minutes. Despite the power of the latter, Aleister Crowley could barely feel the attack, and the vibrations didn't even shake the liquid that he was floating in.

Other capabilities
As the base of the infamous magician and chairman of the city, Aleister Crowley, the building has formidable capabilities that serves its purpose in protecting its sole occupant. Since there are no entrances into the building a teleporter is required as a guide into the building. The building can produce its own oxygen, and is designed to be able to withstand nuclear attacks. Musujime Awaki also claims that it can block radiation from space, and she theorizes that the Windowless Building has other defenses inside, as she is certain that Aleister would not create such a formidable building, only to make it accessible to any teleporter with the skill to enter it. Aleister's room appears to be quite advanced, having numerous display screens that seem to appear out of and float on air. The building probably allows him to connect to UNDER_LINE as well as other monitoring devices that go well beyond that of Academy City, such as those that allow him to monitor the Sisters' status across the globe. The foundation of the Windowless Building is 15 meters below the surface, spreading out for 3 kilometers in every direction, with several thick pillars that head deep undergound. Thor assumed that even with a nuclear landmine, it wouldn't be enough to take it down.

The building seems to be render detection from the Church of Necessary Evil's useless, as they were only able to detect Aleister Crowley's wavelength after he stepped outside of the building to try and kill Fiamma of the Right.

Prior to September 30th, Heaven Canceller was the only one that has access to the means to kill Aleister by shutting down Aleister's life support system remotely. After Vento of the Front's defeat, Aleister removed Heaven Canceller's way of doing so.

There is a large space below the Windowless Building with ramps leading in and a set of rocket engines, suggesting that the building may be intended to leave the planet.

Background
The construction of the Windowless Building and its true purpose remains a mystery. It is both the base of Aleister Crowley that prevents him from being detected by the many magic side organizations but at the same time is the prison of Fräulein Kreutune.

She cannot be harmed and has the ability to learn by scanning her surrounding her environment, and if left uncheck will transform after accumulating enough information, and will eclose into something that maybe a threat to mankind. Her isolation in the formerly impenetrable Windowless Building was to stop her from learning.

It can be assumed that Aleister resides in another section, while Fräulein's prison can be found in another section that can be accessed through normal routes.

Deep Blood Arc
Both the building and Aleister Crowley are first seen having a face to face meeting with Stiyl Magnus, after he is called back from England to deal with Aureolus Izzard taking over Misawa Cram School and capturing of Himegami Aisa. Here Aleister also permits and suggests to Stiyl to use Kamijou Touma, the Imagine Breaker, to aid him in the mission, citing that he is simply a Level 0 and that he is someone that will not be able to leak information from both sides.

Kazakiri Hyouka Arc
The building is featured once during the arc, here it is shown that one requires the use of a teleporter, mainly Musujime Awaki to get inside the building, escorting Tsuchimikado Motoharu to meet with Aleister. Having taken immediate notice of Sherry Cromwell's and goes to the Windowless Building himself to berate Aleister for his lackluster effort at preventing her from getting in. Aleister does not heed Motoharu's concerns, telling him that he is aware of the intruder and use this opportunity to shorten plans as well as strengthen Kazakiri Hyouka at the same time.

After the incident is concluded Tsuchimakado Motoharu asks him if he is happy now that he is now closer to holding the key that can control the Imaginary Number District. After questioning him on giving consciousness to the Imaginary Number District Motoharu ponders Aleister's words, he realizes a part of what Aleister is thinking, and demands to know if he is making an Artificial Heaven. Before leaving, Motoharu gives Aleister advice and warning him that if he continues using the Imagine Breaker, then he should ready himself not to treat him halfheartedly, for surely, his right hand will eat his illusions alive. As Motoharu leaves him alone in that Windowless Building, Aleister tells that the world he believed in was destroyed a long time ago.

Academy City Invasion Arc
After finishing his conversation with Kihara Amata, Accelerator realizes that Academy City and the General Board of Directors are the ones pulling the strings behind Kihara Amata, and can easily pick one of them to find where Kihara Amata is. Angered by the fact that Academy City is using him, Accelerator once again uses Calculation assistance device to attack the building in his rage by throwing a wall at it using five minutes worth of earth's rotational momentum (an entire building in the anime).

In the aftermath of the invasion, Heaven Canceller contacts Aleister to object to his actions, more specifically Aleister Crowley's use of Heaven Canceller's patients such as, Kamijou Touma, Accelerator, Last Order and the clones for his plans. This has greatly strained the relationship between the two founders of Academy City, with Aleister Crowley unyielding in changing his methods, Aleister Crowley severs his ties with the Heaven Canceller, his doctor.

Battle Royale Arc
After the events of the 0930 incident, BLOCK discovered that they may be able to challenge the will of Aleister Crowley. Their plan was to storm the Reformatory using the mercenaries and take hostage of Musujime Awaki's comrades that have been kept there as a leverage to force her to cooperate with them regarding the secrets of the Windowless Building, Aleister Crowley's base, which would then, if successful, allow them to execute their masterstroke, transport a Synchronous Multilayer Bomb into the building itself and assassinate him. Despite their preparations and actions, their plans are later foiled by the actions of GROUP.

Ichihanaran Arc
The main objective of Kamijou Touma and Thor is to break Fräulein Kreutune from the Windowless Building. Despite having the feat of withstanding even Accelerator's georotational momentum powered-attack, Touma and Thor manage to crack the Calculate Fortress using a jackhammers after calculating the weaknesses of the Calculate Fortresses' impact diffusing abilities, and is later broken completely by Fräulein.

After Fräulein escapes and Touma and Thor regains consciousness after being attacked by Fräulein, the both of them are later tempted to go inside the hole Fräulein made, but manages to snap it out as so they can catch up with Fräulein.

Mental Out Arc
Kihara Noukan contacts Aleister Crowley in his stronghold and informs him of completing his 72nd and final request of Aleister of dealing with and eliminating groups or persons that have grew during his absence and refused to regroup. Noukan questions Aleister about his choice to fight the magic gods and debating each other feelings of emotions and romanticism as scientists. Noukan then asks that now that he has returned order to his rule as he has tasked him, he requests that he should use the power he has returned to him to destroy all the irregularities known as magic.

Salome Arc
When Misaka Mikoto attacked Kihara Yuiitsu with the Anti-Art Attachment in order to save Touma, the Windowless Building acted as a cushion and prevented the damage from spreading across the city. Not long afterwards, as Yuiitsu turned towards the building with World Rejecter in hand, Aleister came out of his safe zone and confronted her before turning to the other problems at hand.

Element Arc
While Academy City was swarmed by the Elements, Yuiitsu hid in the space below the building, waiting for Kamisato Kakeru and the Kamisato Faction to emerge. A confrontation between the two occurred in this space on the morning of December 9th and the rocket boosters were used as a final trap by Yuiitsu, forcing Kakeru to use World Rejecter with conflicting desires to protect the group from the igniting engines, exiling himself in the process.

Daihasei Festival Arc
Following Misaka Mikoto's first transformation as a part of Kihara Gensei's experiment, Kouzaku Mitori brings out her fears and anger towards the city, and has her attack the Windowless Building, saying that as long as that command tower at the center of the city exists bad things would happen and someone will always get hurt. Mikoto complies and uses her new found power to make an incredibly powerful beam of electricity descend from the overcast sky, though the Windowless Building survives. Gensei calls Mitori that in spite of Mikoto's power, she cannot damage the building by attacking it head on. Gensei then says that her current state is that of 2% along the path of a Level 6.