Italo Calvino's Invisible Cities is certainly not a standard, typical fantasy book. Not an epic with wizards, dragons and barbarians. But it's the best piece of fantasy fiction I've ever read - even better than Borges' "The Aleph", which comes in second place. At each chapter, Calvino pushes human imagination to its furthest boundaries, challenging the reader's concepts of reality, history, ethics. I just can't stop reading it over and over.