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.

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.

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. 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.

Deep Blood Arc
Both the building and Aleister Crowley are first seen after Stiyl Magnus is called back from England to deal with Aureolus Izzard taking over Misawa Cram School and capturing of Himegami Aisa.

Kazakiri Hyouka Arc
The building is featured once during the arc during Kazakiri Hyouka's manifestation into Academy City. Here, it is shown that one requires the use of a teleporter, mainly Musujime Awaki to get inside the building.

Academy City Invasion Arc
{Main|Academy City Invasion Arc}} The building is prominently featured during the arc, where it is shown to withstand Accelerator's attack without a scratch.

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 weaknessess 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.