The librarian gathered her wits about her, thumbed the stack of index cards in her pocket and nervously touched the ball of twine at her belt. She had seldom descended beyond the third circle of the Library before, but she was the only one on duty and this was urgent. The stacks changed down here. The books were wild and old, and the atmosphere heavy, but this was only the third circle. The book she needed was deep down in the fifth circle, so said the cards. Down there with the minotaur.
She played out more twine, navigating around a space-bending circular shelf of grimoires, under the stone arch and down stairs to the left, into the fourth circle. Down here, she knew, were elder-scrolls and magical books that only existed when you looked at them out of the corner of your eye, plus other dangerous wonders. There appeared to be a dark cloud overhead, flashing occasionally with purple lightning, but again only at the edge of her vision. The special wire-rimmed glasses helped keep everything in order right ahead of her. Without them, the books would be conjuring up nightmare images to frighten her away. These books do not like to be read. And still she had to go deeper, following vague clues in the cards and what few signs the Master Librarians of years gone past had managed to leave behind.
It was the third Master Librarian, Mugu, who had discovered the five-dimensional Dewey Decimal System underlying the library's structure. Few other librarians had risen to his level of mastery, possibly because his notes had to be kept here in the fourth circle, where the numbers on the stacks danced and played, never quite looking like numbers unless you knew how to look at them (and could do higher-dimensional library-calculus in your head).
She almost missed the door to the fifth circle in a tiny crack between the stones of the inner wall, halfway around, and had to use an index card incantation to fold herself between them and into the fifth circle. The gravity change was abrupt and unsettling. She was walking on the inner surface of the wall and had a stone floor (or ceiling?) to her right. On the left was a field of stars, offering the only light, and that very dim. The bellow of the blind minotaur roused her from her fascination. She checked her index cards again, performed some calculations, turned three times in a circle and deftly plucked her book from the half-invisible shelf mid-pirouette. She folded herself back through the impossibly narrow staircase just as the minotaur zeroed in on her scent and gave another mighty roar.
The trip back to the binding desk was relatively easy, though it did feel like squeezing her brain into a jar to return from those extra dimensions. She arrived famished, but first needed to clamp the book to the desk, lest it escape. It was vibrating slightly, clearly nervous to be out of its (super)natural domain, so she incanted some soothing mnemonics and it quieted down. Handling books and minotaurs, after all, was her trade. Readers, however, were something truly terrifying.
Mokalus of Borg
PS - I quite like Terry Pratchett's writing about the Discworld's Unseen University library.
PPS - And most of his other stuff, too.