But the idea that the pool had fallen into the library just had not occurred to me.

For some reason the idea that it had all slid down in a glorious mess of water and books and Doctor and probably other stuff upon crash landing, hit me pretty early on and amused me. I imagined it like the Titanic upending and everything sliding down to the end (though in my mind it was the whole pool, not just its water), then I thought maybe the pool just liked to wander and then I guess I subscribed to the theory of 'pool lives in the library'