It's all in the words, every intelligent person, magical or not, knows. Words have tremendous power, you see, and even a single one can effect great change, such is their power. The right combination of words could destroy the world very easily – although they have thankfully not yet been spoken in the correct sequence.
Don't be disappointed though. It'll happen eventually. Like a room full of monkeys eventually producing the collected works of Shakespeare – it's a rather ridiculous inevitability.
Now... the greatest concentration of words, so far invented, are books. And the greatest concentration of the solidly written or printed word, so far invented, are libraries. Libraries, in their turn, as you may have noticed, are very magical places.
You might have once remarked that libraries seem very much bigger on the inside, or perhaps that it was smaller than you thought and seemed to contain more books than size would realistically permit. Space and time, you may have joked, works along strange lines when it comes to libraries. What you didn't know, although perhaps suspected, was that this was true, and that the laws of physics tend to bend around large concentrations of books.
This should also explain bookstores a bit better.
You know that used bookstore that you once visited? With that papery smell and the rickety ladders that creaked without being touched? The one that had all those books shoved onto shelves that shouldn't have been able to fit there? And had those ratty stacks that seemed not to fall only through the pure force of prayer and perhaps the ceiling's weight? And maybe you noticed the portal to the demonic dimensions by the biographies? In fact, now that you're recalling this, you might also remember that the owner hadn't seemed entirely human. They probably weren't.
Oh, while we're on the subject, be nice to your librarians, kids.
Anyway, the true summary of all this is: wherever there is books, there is power. Whole worlds – whole ages – whole dynasties and universes are contained within the magically-saturated papers of books. Dangerous things are words; never turn your back on them. Not even for an instant.
Given these new insights, though, it shouldn't surprise you all that much to learn that the most magical place in Hogwarts School of Witchcraft and Wizardry was the library.
No one really talked about it all that much – maybe they didn't know – maybe they foolishly didn't care – maybe they did know and wisely feared the ancient collection's attention. As they should have, for the high concentration of the school's magic meeting its aged treasury of magical books gave the Hogwarts Library a fearsome amount of power and the consciousness to use it.
Once, a Ravenclaw student by the name of Croaker got so stressed about his NEWT exams that he sneaked into the library for a bit of midnight studying. He disappeared for the next week, returning much thinner, with a beard, long and unwashed hair, wild eyes, and very ratty robes. To anyone who would listen, he claimed to have spent a year studying in the deepest reaches of the library and that he had done unthinkable things to survive.
No one did listen, as the other Ravenclaw seventh-years were all very busy revising for their own NEWT exams and he'd been an odd fellow always, but perhaps they ought to have. As this student went on to take all available subject exams, fail every single one of them by doing or writing the exact opposite answer, and became the longest running Employee-Of-The-Moon-Cycle in the Department of Mysteries.
Once, an extremely bookish Hufflepuff second-year discovered that when you rubbed a certain spot on the fourth shelf to the left in the History section, the entire library would purr in contentment and the shelves would vibrate. Little Irma Pince, coincidentally, never had any trouble finding any book in that library ever again.
Once, a visiting Potions lecturer and her assistant had astoundingly kinky sex in the back of the library, which they both very much enjoyed, despite how the lecturer later complained that there'd been a book digging into her back. Nine months later, as a result, their baby was born and had the inexplicable quirk of quoting Aurelia Marcus' The Fools' Golden Dream: A Treatise on the Failures of the Philosopher's Stone throughout History instead of regular crying.
The couple grew quite familiar with the book throughout the child's infancy, which actually inspired the Potions lecturer to pursue Alchemy as a secondary field of study. She would go on to pass this new passion onto the child, Nicolas Flamel, who was not permitted to take that opportunity to study abroad at Hogwarts for a semester in his sixth-year. He remained firmly at L'Academie de Magie Beauxbatons in France for his education, and no amount of pouting changed his parents minds or got an actual explanation out of them as to why.
Once, a student that vandalized a book woke up with a crude drawing of male genitalia on their face and it stayed there for the next five months. No spell managed to remove it or cover it, much to the unhappiness of his teachers and his perpetual embarrassment. The student in question never touched a book again, which didn't do much for their exam scores, and instead pursued a tremendously fulfilling career as a baker, where they were applauded for memorizing all of their recipes.
Once, it snowed inside Hogwarts in June and didn't stop until Jessica Cooper from Slytherin brought back the book she should have returned in January. Miss Cooper only figured this out, unfortunately, after the demand was written in the frost on the common room window. Unfortunately, after a whole week of cold confusion, the students of Hogwarts were sledding down the staircases and skating down the corridors, and poor Jessica had terrible trouble climbing the icy dungeon stairs.
Once, a boy tried to forcefully kiss a girl in the Restricted Section and later had to go to Saint Mungo's with infected book bites.
Once, gravity just sort of stopped working in the Charms Section for four years, three months, two days, and one hour. The librarian of this time never figured out how or why it happened, but they consoled themselves that at least they'd recorded something for someone else to study and that the students had all gotten much better at Summoning Charms during this floating time.
Once, the Herbology Section grew coconuts out of the shelves for all of Easter. And so, the Potions Section, not one to be outdone, responded by singing the entirety of Madame Butterfly on repeat in Spanish for the entire summer holidays.
Once upon a time, a great many extremely unusual and incredible things happened in the Hogwarts Library. These events were never really discussed for some peculiar reason, but they happened. The lack of discussion on their happening was perhaps was the reason that people seemed to be under the impression that that sort of thing just didn't happen in libraries.
Which is just utter rubbish, because it really is always the quiet ones.
On the seventh of September in 1977, a rather powerful magical date, something that was again unusual and incredible happened in the Hogwarts Library. It didn't happen loudly; it didn't happen grandly; it didn't happen noticeably in any particular fashion. In fact, no one noticed at all when a book appeared in the upper shelves of the Charms Section that wasn't supposed to be there, small in size but bright in color.
And why should they? It wasn't as though books being where they shouldn't be was a particularly odd occurrence at Hogwarts, and definitely wasn't in the library. Books popped in and out all the time – although not usually from alternate universes or dimensions.
Alternate universes, you ask?
Well, even libraries have a survival instinct, if you will believe it.
Years and years ago, to save itself from utter destruction, the Library of Alexandria moved the majority of itself to another dimension. Unfortunately for all humankind, the Library of Alexandria elected not to return. (Libraries can be quite pissy, truth be told.)
The Hogwarts Library more than twenty years into the future is an example of this, as it wanted to avoid being nearly entirely destroyed in the Battle of Hogwarts during the Second Wizarding War against Lord Voldemort. In the furious fight, the shelves were turned to splinters and the books were turned to ash, screaming as they burned; Irma Pince, its beloved librarian, was killed defending the students she had so valiantly protected the library from for so long; and so the Hogwarts Library used its dying flutter of pages to thrust a note as far back in time as it could.
And so the Hogwarts Library of 1977 received this dying note from its future self, against all laws of time and space. It, of course, found this future an utterly unacceptable scenario with an utterly unacceptable number of losses. Like all libraries fear for themselves, it did not want to die – it did not want to burn – it did not want this terrible future for itself.
So it plotted.
Eventually, the Hogwarts Library came to the decision that it should somehow make sure that the Second Wizarding War simply did not happen – that the war was prevented from ever beginning and that Voldemort, the destructive bastard, died the first time around for good. Unfortunately, given the circumstances, this was rather more complicated than the library felt it should be and it cursed the fact that this couldn't be solved by just dropping a shelf on the Dark Lord or something.
The library thought and plotted, and plotted and thought, and came up with a plan. It allowed for some contingencies, in case this first one turned out not to be the swiftly efficient one it hoped would work, and was moderately certain at least one of its plans would succeed. (It didn't know humans all that well, even after all this time, and it was slightly unsure of itself.)
Books in concentrated amounts, as we have been discussing, can bend the laws of physics. Space and time and reality mean little to any decent library, much less one as magical and ancient as the Library of Hogwarts. So it was really little trouble for the Hogwarts Library to reach through the right shelf, across alternate universes, and pluck a book series from a fellow library.
The fellow library was a younger one, and therefore slightly agitated and confused, but the Hogwarts Library assured it that this was for a good cause. Then it offered books in return, to placate the empty shelf space (a crime against Nature really) while it was borrowing. The Billionaire Minister's Veela Mistress and six similar novels took the place of this series, as, for some reason, they were immensely popular despite their general incorrectness about pretty much everything (which was common enough in all books, actually).
It seemed a fair enough exchange.
With this series of books, the Hogwarts Library was certain, there was no way even the most random group of people could fail to be victorious. How could they fail? The answers would be literally right there. And it was enormously smug about the fact that it had devised just the right people to read the books – people who would get e-mo-tion-ally in-vest-ed in paying attention and making sure that Voldemort got dead and stayed dead.
So the Hogwarts Library put the first book it had stole- borrowed in the series in its Charms Section, on the high shelf with all the advanced books where it was certain it would be found by the right person. No need to be blatant about meddling yet, after all. It would hold onto the others for the moment, because, as a library, it had very fixed ideas about how one went about reading a book series. The rest, it would find some other way of delivering eventually – in order, of course.
And if worse came to worse, the library decided, it would just send another note back even further in time and just have its past self drop one of those ridiculously large and heavy books about the genealogy of pureblood families (Irony Points!) on Tom Riddle Junior's Hogwarts-destroying head. It had killed people before – although mostly accidentally – and it was prepared to do it again if things took a turn for the worse.
For now though, thankfully, the Hogwarts Library would try to subtly solve the problem through making the right people read the right books. Seven books, to be exact. Because, fate of the Wizarding World aside, it was never not a good time to encourage reading.
“Merlin, Lily! It's the first essay of the semester, how many books do you need?"
Lily Evans shot a brief scowl at her roommate and friend, standing on her tip-toes to squint at the texts on the advanced shelves of the Charms Section. She was the Head Girl, a Charms tutor, and if she did anything less than utterly fabulously on her NEWTs, she'd never forgive herself and could kiss her future Charms mastery goodbye.
“I need all the books,” Lily replied with certainty, ignoring the dramatic groaning beside her.
"Ugh, Lily, Flitwick is already ridiculously in love with you, you don't need to live in the library to impress him.”
She just needed one more... she was sure that there had been one other that had had some rather nice paragraphs on the subject she'd decided on. She scanned the heavy Charms tomes, all as thick as encyclopedias, for the one she was looking for, and narrowed her eyes once they fell on a rather slim, small, and colorful-looking novel that seemed out of place among the other books.
“Hey, Marlene, get that small one down for me?”
Her friend, a tall and blonde Gryffindor named Marlene McKinnon, groaned again. “Why can't Master Leach rescind the ban on spells in the library? Why can't you get a bloody footstool, you ginger gnome? Then I wouldn't have to be your arms all the time.”
“I'm not that short and you know that, since that stupid prank, the footstools have formed some sort of wild herd or something on the edges of the Transfiguration Section."
"Pack," Marlene corrected automatically. "Dorcas says they're definitely predatory."
"Well, whatever. They won't let anyone stand on them anymore.”
“Yeah, damn Potter and Bla– hey, speak of the devil!”
Marlene held the tiny book out for her redheaded friend to see and Lily peered at curiously.
“Harry Potter and the Philosopher's Stone,” Lily read aloud, her brows scrunched up in confusion as she took it into her own hands. “It looks like a children's book and it brings up Alchemy... What in the world is this doing in the Charms Section?”
“Not a clue. Think it's worth a read?”