…No sensible person would try to fit four elephants on top of a fish. Which leaves turtles. Small turtles spend a lot of time on rocks, but no one in their right mind would expect a small turtle to hold up four giant world-bearing elephants. Big turtles come out onto land to lay their eggs, but that’s a mystical event and it doesn’t cast serious doubt on the theory that a turtle’s natural place is water. Where, please notice, it does not require support. It can swim. So it stands to reason that any self-respecting giant space-faring turtle will swim through space, which implies that it needs no artificial support to avoid falling.
Why world turtles make the most sense for planets to rest on, The Science of Discworld, Book IV: Judgment Day. (via sobrighteverywhere)