A book that would be well worth tracking down and fits the bill perfectly is Midnight at the Well of Souls by Jack L. Chalker. It involves an extinct super-race that left behind the mysterious Well World, a planet that contains thousands of independent environments, each with a different species (including humans). Our protagonists, including the enigmatic cargo ship captain Nathan Brazil, end up getting sucked through a portal, changed into different species, and deposited on the Well world. Intriguing, imaginative concept & well written. There is a whole series of Well of Souls novels.
Last edited by usuallee; 04-18-2013 at 10:39 AM.