Terry Pratchett's Discworld series is a large series of books that tell the story - or, perhaps I should say "stories" here? - of events that unfold on The Discworld. The Discworld is a planet in the shape of a disk, which rides through space on the backs of four ENORMOUS elephants, who themselves are riding through space on the back of a GIGANTIC turtle. The discworld is a magical place full of wizards, witches, trolls, dwarves, and various other creatures. A world where unusual occurances aren't actually all that unusual.
It's a fantastic series... At least, I think it is! But, if you want to read the books and find out for yourself how good they are, then you can find a list of the books in the series - as well as most of Terry Pratchett's other books - in my Terry Pratchett books post, which I actually posted over a year ago.