The Last Continent by Terry Pratchett

This book finds Rincewind making his way through FourEcks (EcksEcksEcksEcks), a continent that looks a whole lot like Australia, while on the other side of the Disc, the wizards who sent him there are trying to figure out how to get him back (as the University librarian, who was turned into an ape some time ago, has gone unstable in his shape, and the wizards need to know his name to perform magic on him--a name which only Rincewind has a chance of knowing). But in their search for a geographer to help them find XXXX, they step through a window that takes them to a different place and time, where  they encounter a small god, who keeps banging his head against evolution. This was not one of my favorite Discworld novels (though in all fairness, Pratchett's take on academics is pretty funny)--I think it's because Rincewind has just never clicked with me as a character. But there were definitely some pretty funny moments along the way.