The Magician King by Lev Grossman
Meet Quentin Coldwater, king of the bizarre and wonderful land of Fillory. But he is getting restless, even in heaven a man needs a little adventure. So when a steward is murdered on a morning's hunt Quentin gets exactly that. But this quest is like no other. What starts as a glorified cruise to faraway lands soon becomes the stuff of nightmares...
The Magician King is a grand voyage into the dark, glittering heart of magic, an extraordinary journey that allows the imagination to run riot and proves Grossman is the modern heir to C.S. Lewis.
This is a book like no other.