The Light Fantastic written by Terry Pratchett performed by Nigel Planer on CD (Unabridged)

The Great A'Tuin, the heroic turtle who supports the weight of the entire Discworld, not to mention four giant elephants, swims through the galaxy day and night with the burden of being the only creature who knows exactly where the universe is going. Philosophers have long debated where this is, and are due to find out in about 2 months. Shall they worry? Well, they are on a collision course with a malevolent red star and only one person can save Discworld.

Unfortunately, it's the cowardly wizard, Rincewind, who was last seen falling off the edge of the planet. This is the second book in the Discworld series.