The Haunt of the Great Library

By all evidence, Great Library of Adventurers' University of Caldonia is at least 1000 years old, and its proprietors claim several times that. In that amount of time, any building is likely to gain a few haunts. Libraries are more susceptible than most structures.
It is therefore safe to conjecture that there are many haunts in the library -- from localized poltergeists and possessed books to focused, non-terminal, repeating phantasms. But when students at AUC refer to The Haunt, there is not a question of what they mean.
Some years ago, there's no documentation that can identify exactly when, the School of Comparative Abominations formed a joint research project with College of Eldritch Science's Summoning Department. Equally lost are the records of what the research was intended to uncover or understand -- much less the specific experiment they were performing in the Cosmicthonic Provenance wing of the library. What is known is that it was very complicated, involved sufficient quantity and complicated sigils that professors of cartography were called in from the College of Piracy, and required a good deal of complicated machinery from Trap Research and Development.
All told, 35 professors, 15 laborers (undergraduates), and 3 grad students were present on that fateful night.
As expected, and most likely as intended, an unfathomable presence was summoned, most likely from another reality or existential plane. The cause of what happened next is uncertain, but the leading theory is that a number of sigils were drawn in reverse, possibly on purpose (pirates are notorious pranksters). So chaotic was the summoned entity (or entities), that it hungered for something to make it complete. In a development completely unexpected, but in hindsight made more sense than anything else that night, it absorbed all of the intellect in their immediate vicinity, including the accumulated books and, as it happens, the organizational system of the library.
Watching all this happen, the minds of the 53 university personnel shattered at an assortment of speeds, leaving bits of mind and soul scattered throughout the area. The newly formed haunt, hundreds of books, the Gesneri-Garampi Index Archivii system, and approximately one eldritch horror, immediately set about the task of organizing all the component bits of psyche and soul leftover from the disaster. It continues the task to this day. When it discovers someone has entered the Comicthonic Provenance wing it seeks them out, restrains them, determines how to sort them (preserving the pieces of psyche that break off as the victim observes the gibbering thing), and then shelves the bits and pieces as appropriate.