This YA Fantasy Is a Love Letter to Magical Libraries, read the interview with Margaret Rogerson. 

I read this recently and really liked it. Granted there are other books with magical libraries which I'm sure I'll like even more. History will repeat itself: I read and really liked the first Throne of Glass and then I read The Poison Study which I loved even more! So I'm sure Ink and Bone or The Invisible Library will come become next favorites. Did you read any of them?