The worst book I’ve ever read is probably a book called "Les fiancés de l'hiver". To be fair, it isn't bad; it's just the book I've enjoyed reading the less as I got really bored reading it. This books follows the story of a girl able to go through mirrors she saw herself in. The story starts off as her being in her not so loving family and then she is sent into a giant floating castle to marry an unknown man, who turns out to be a big cold man she doesn't appreciate. Into this giant castle/town there are some deep secrets and mysteries she tries to uncover and understand. Unfortunately I haven't read to following 2 volumes to tell you more about it.
Honestly, I disliked this book because at some point it got so boring and so detailed in the description I considered dropping it off. The end was slightly more entertaining but it was definitly wasn't enough to make me buy the next volume.