Paolo Greco of Lost Pages is collecting a gallery of the Cthonic Codex, showing all of the hand-bound books that he is creating for those that purchased a copy of the special edition of the publication. Theses individualized and custom books not only look beautiful, but show the amount of work involved in binding books by hand instead of going through the automated process that many publishers use today. Each of these books are stitched rather than glued and make with such detail to attention that it’s fantastic to see each of them being created. You need to see the entire gallery in progress to appreciate it and come back to it regularly.
Seeing these books in this format also gives and idea of what books in your fantasy settings can look like. In most settings there’s no industrialized publishing system in place yet books and tomes are commonplace for magic users and scholars, many of them making their own. Consider this gallery for inspiration if you want to include some sort of custom book in your games.