Although for much younger readers, I recommend The Edge Chronicles. The detail and depth of the world really captured my imagination as a child. Seeing the story progress, the effects of time, the ageing and death of beloved characters, the shifting and changing of the environment, as well as the many unique and interesting races made for an all around immersive read. The illustrations too, are fantastic.
The series are what got me into world building, specifically the mechanics of it. To create something of magic with its own brand of physics propping it up, to have every aspect explainable by enough scientific reckoning so that it feels not only plausible, but probable, is a must for me to fully enjoy a book. I can appreciate good writing as much as the next person, but it's the universe and the characters held within that truly inspire me to explore more of the author's works.
Though again not a single book, Terry Pratchett has a lot to offer if you're after a bit of the bizarre with an extensive world and colourful characters.