Suggest me a book that features multiple different worlds

I'm developing a story that involves the concept of there being multiple different dimensions/worlds, and it does a involve a lot of traveling between them, so I'm looking for books that have a similar concept so I can use them to learn how to write it effectively in my story. Fantasy would be probably my most preferred genre, but any genre works really. Bonus points if the main character has no idea these words existed before the story, so the whole things a new experience for them.