books about books (stories within stories)?

i just finished the starless sea by erin morgenstern and really loved it – specifically the stories nested within the main story & general romanticization of books/stories. it reminded me a lot of the orphans tales books by catherynne m valente, which also have nested stories and is just an incredible love letter to folktales and myths and oral traditions. i would put the neverending story and inkheart both in this category as well.

so – i’m hoping for some recommendations that have that same energy! ideally a mystical type of setting (i’ve seen some drier recommendations and am not too interested in less ‘fun’ books). i don’t mind if they’re aimed towards a younger audience as long as they aren’t condescendingly simple.