148 An enormous collection of cheap and trashy romance novels in a variety of forms and languages. The only real connection one can extract is that each involves a magic using character in a main role.
Upon actual reading of several of the books will their real purpose be realized: Each book is a tutorial on how to learn a particular spell! One must read the misspelled words, substituted for very similar words, and follow components in accompanying text. learning the spell this way is effectively taking a 20.
The size of the library is up to the GM, but my players found over 200 books in at least ten languages, several no longer in use, with a quantity of overlapping spells. For example, these involved several languages with differing version of prestidigitation or its earlier spells from previous editions. This included a Rube Goldberg kitchen set up to fry an egg, provided by a player to flesh out the list. See the opening titles of Elementary for a current example. Another player included a book with a number of Dwarven Crafting Chanties that yield +2 bonus to non-magical folk using all three components for each skill.
My 'clue'? the first book they examine was titled: 'A Spell Learnt' by one Procter Joneth, Instructor of the Primary Foundations of Science and Learning (a mythical teacher, surely all these books are fakes!). All it really dealt with was how to clear one's mind and focus on drawing control of magical energies into your control, even if you have no talent for magic (You rely on all three components to gain access to magic).
I hadn't planned it, but the players a few dozen additions at the next game, including a booby trapped version of invisibility, with the victim learning a version that acted as an Undead summoning beacon. That was fun!