Lucas discusses one of his favorites: Out Of The Silent Planet by C. S. Lewis. It offers a classic sensibility on science fiction while providing an interesting perspective into a possible spiritual reality that spans the entire solar system. Get the book here.
Actually, CS Lewis didn't believe he wrote allegory. He said he had already in his mind pictures of a world like Narnia and it came as he wrote. Instead, he says it's a book about 'supposing'.
""You are mistaken when you think that everything in the books 'represents' something in this world. Things do that in The Pilgrim's Progress, but I'm not writing in that way. I did not say to myself 'Let us represent Jesus as He really is in our world by a Lion in Narnia': I said 'Let us suppose that there were a land like Narnia...'".
https://www.thegospelcoalition.org/article/why-narnia-isnt-allegorical/