In the city of Limen, there is a Ghost Library.
The Dwarves Chroniclers had built a huge tower, the Mountain Cyclopaedia, and when the Dragons came to steal the One Book, the Dwarves burnt their whole Library, lest the Dragons could use it.
But there is still a shadow of the Library (in the akashic records of the noosphere). If you can enter the Library of Ashes, here are a few rare books you could find.
Roll a Dewey Decimal Die:
1 Psychology: Raven Lady, The Book of Empathy : This books can give you the power of Empathy. The very rare first edition has a drawback: you share all the emotional states of the writer and have flashbacks about her death. Other editions can make you connected only to the other readers of the book.
2 Religion: Pyrephlegeton, The Refutation of the False Essences : the best atheist book ever written. It makes the Reader entirely resistant to clerical suggestion and gives a +25% resistance to all Divine magic.
3 Law: Anonymous, The Digest Compilation of Forgotten Jurisprudence. If the reader is a good orator, he should win any legal case with this collection. Else, you can sue the book, according to the old Euathlus lex.
4 Language: Urania, Lexicon of the Stellar Lyrics. There is a constant Music of the Spheres but most people don't pay attention to it. With that dictionary, you can understand what the Stars say at night.
5 Natural Science: Coincidence of the Opposites : the recipe of firewater ("Greek Fire"). The Library of Ashes will magically expel anyone who tries the book within the premises.
6 Technics & Medicine: Dr Gepetto Honeststone, De Arte Corporis Animandi (or, So You Want to Create Life and Challenge the Creation Itself?): You need another book (the Azimoth Amendment) to be sure the Flesh Zombie won't have a huge Oedipus Complex against its "father".
7 Arts: Anonymous, Runes on My Body: a very heavy tome of calligraphy and tatoos, made of dragon scales. The sentient tatoos have different powers but each tatoo gives 10% of likelihood of Possession by the Dragon.
8 Literature: Calmer Stupor, Time regained. Very enticing book but with a weird temporal anomaly. One hour of reading for the reader takes one week of common time. It takes 1d10*1d10 subjective hours to finish it (and you really have to).
9 Geography: The Braille Map of the Invisible Cities.
10 Information & Libraries: The Hellindex, vol. XIII: each page contains a dimensional gate to the forbidden rooms of the Library. Go to Call of Cthulhu and lose 1d10 SAN.