The Door in the Wall by H.G. Wells may actually be my favorite short story of all time. It captures all the magic of Narnia but with a more adult sentimentality. It embodies, in a much shorter form, some of the complexity of personal morality one finds in Frankenstein, Dorian Grey, and Jekyll & Hide. It makes me think about the nature of fantasy, and religion, and regret, and joy. It's simply a great little story, perfectly told.