WooHooMan
Auror
I'm thinking of using Watership Down as the source for my Outer Sphere, with the twist that the forests, animals and fields are huge while the Dreamer, the Somnolents and Naimar remain normal size. The animals can talk, so they're part of the story in a real way. I haven't read the book though, I only watched an animated version of it as a child.
That's one of my favorite books.
I would kind of prefer you don't use it. You should probably stick to something more public domain.