Warning Spoiler Alert: This article or section contains details about plotlines not covered in the anime. Do not proceed unless you wish to be spoiled.

The Great Library Room (大図書室, Dai Tosho-Shitsu?) is the library of the Central Cathedral in Underworld in which Cardinal had taken shelter before the final battle against Quinella (Administrator) at the top of the Cathedral.


The walls and ceiling of the ten meter long hallways of the library are covered in antiquated wooden boarding. At one end of each hallway, atop a tremendously steep staircase is a small plain wooden door, which in contrast to the antiquated hallway, is made from brand new plain wood. These hallways do not have a source of illumination of their own, with only a faint light coming from the next room. The entrance room connecting over 10 hallways of the Great Library Room is a considerably wide, square-shaped room.

The actual library is an absurdly large room that is comprised entirely of bookshelves and books spread out infinitely. It has a stone dome for a ceiling, a cylindrical wall, which seems like it is made out of plain bricks, with many layers of staircases built on the walls’ surface. The distance between the ground floor and the canopy of the library - on the other side of the long gallery that stretches out like a multi-storey maze - is easily at least 40 meters, corresponding to the size of a ten-storey building in the real world. Somewhere within the frequent forks and slopes of the bookshelves is a circular space, with a table and two chairs in the middle of it. One of the paths also leads to a bathroom. The air within the library is filled with a dry smell, reminiscent of timeworn paper.


The Great Library Room was created by Quinella after she found out about the limit to her memory. The Library was used as an external memory storage, where Quinella stored her extensive memory data related to all system commands and the history of Underworld itself in books, although the version stored within the library is the one fabricated by Quinella.

Great Library Room

The Great Library Room constantly changes where it is located.

To prevent anyone else from entering this room, Quinella made it within the Cathedral, but not spatially linked to it, by using a system command to make the coordinate values of the library’s space constantly change to random numbers in the unused regions of the system. Only a single door that existed at the time the library was separated from the Cathedral could be used to enter the hidden room. The door could only be called out after reciting a special command that only Quinella and, later Cardinal as well, knew and could also be locked from the inside by turning the key in the lock 90 degrees to the right, while unlocking it from the outside required a tedious ritual to be chanted.

However, after Cardinal retreats to this library, she destroys the original door, the only method of entering the library, to prevent Quinella from accessing the room. Although the library’s coordinates are ever changing, the Central Cathedral’s coordinates are fixed, allowing Cardinal to create multiple backdoors to the Cathedral that she could use to send her familiars outside of the library, as well as to allow chosen individuals to enter and exit the library if needed. Each backdoor can only be used once, as Quinella’s familiars are able to detect it upon it being used the first time.

Since the Great Library Room is an isolated space, it has a very limited supply of resources, greatly limiting the creation of items within the library. Therefore, the books stored within the library are usually used as a sacrifice when the need to create basic items arises. The creation of high-priority items, however, requires a much more significant sacrifice than books, so such items can only be created within the library by sacrificing an object that is brought into the library from the outside.


Alicization ArcEdit


After Quinella gained an advantage in her battle against Cardinal, the latter was forced to retreat. With her life at stake, she started chanting the ritual for calling out the door to the library and, even though she was obstructed twice, she finally managed to complete the ritual and summon the door, locking it up as soon as she was inside. While Quinella attempted to chant the ritual for unlocking the door from the outside, Cardinal chanted a ritual for destroying the door. At roughly the same time as Quinella finished chanting and unlocked the door, Cardinal finished chanting her ritual, blowing the single entrance to the library into small pieces. After that day, Cardinal secluded herself within the library room for over 200 years, only sending out her familiars to look for a collaborator capable of assisting her in fighting Quinella and devoting the rest of her time deliberating about the world.

Alicization TurningEdit

After Deusolbert Synthesis Seven intervenes in their battle with Eldrie Synthesis Thirty-one, Kirito and Eugeo navigate through the Central Cathedral's rose garden in an attempt to escape from the attacking knight. However, they eventually reach what seems to be a dead end and are about to meet their fate, until they hear a young girl with an elderly voice calling them, making them notice a door which they did not see before. The two young men quickly jump through the door and are surprised to find themselves within a wooden room. After the young girl locks the door and gets them to leave to the next room, she seals hallway to prevent Quinella's familiars from gaining access to it. The girl then leads the two shocked boys into the Great Library Room, where she introduces herself as Cardinal, offers them snacks and frees them from their chains. She then has Eugeo leave her to chat with Kirito alone under the convenient excuse of Eugeo treating his bad flu status and getting to read history books. After Eugeo leaves, she leads Kirito to a circular space with a table and two chairs, where she begins telling him her story of how Quinella came to power.

Alicization RisingEdit

Kirito and Eugeo spend several hours in the library room while they recover and Cardinal explains the history of Underworld, Quinella, and herself to Kirito. In the meantime, Eugeo recovers from his bad flu status and spends the time reading history books within the library, with the hopes of finding an instance of someone who opposed the Axiom Church and managed to safely escape after fulfilling their wishes. When Cardinal finally finishes her story, she makes a deal with Kirito, and then teaches the two young men how to use the «Armament Full Control» Sacred Art for their Divine Instrument class swords. She also gives them two daggers, which they could use to rescue Alice and defeat Quinella. Afterwards, Cardinal leads them to the library's backdoor that is the closest to Cathedral's equipment vault and the two youngsters leave the Great Library Room to reacquire their weapons and ascend to the topmost floor of the cathedral.


Underworld Locations Navigation Bar
Centoria Central Cathedral - Great Library Room - Sword Mastery Academy
Norlangarth North Empire Gigas Cedar - Rulid Village - Sword Mastery Academy - Zakkaria
Mountain range at the Edge North Cave - East Gate - South Corridor - West Gorge

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    • 超巨大図書室 超<--adverb, meaning: super 巨大 or 大<-- adjective, huge/large 図書室<--noun (not a proper noun) ---...
    • Eh.. This is an old and resolved issue...
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