Hello <p>Hello dear friend,
I friend,<br><br>I have been investigating about this books for some time, after looking your question and i only found this books relateds with library!
Zathroth's library!<br> <br><br>Zathroth's Library - Found in Isle of Kings
The Kings<br><br>The Ferumbras Files - Noodles Noodles Academy of modern Magic
Library Magic<br><br>Library Key - Desert Dungeon (we are not sure if this book is talking about zathroths library)
About library)<br><br>About Lord Lokhem - Carlin, found in one bookcase in paladin guild.
Thats guild.<br><br>Thats all books i found about LIbrary of Zathroth or secrect library!
I library!<br><br>I hope i helped u,
Gleemodyu,<br><br>Gleemody<br><br>Pd: Remember that u can check all the books in game in this <a rel="nofollow" href="https://elkolorado.github.io/tibialibraries/">TOOL</a>.<br>There u can search all the entrances u need, i checked for: Zathroth - Library (i found a lot of book from diferents librarys) - Secret library</p>