Here's a weekend post which delegates creativity to you.
Anyone who's read Lewis' Great Divorce knows he was enough of a believer in second chances to have re-invented purgatory. What if there had been an 8th Narnia book? What would the title and basic plot have been?
Rules: It must take place, at least in part, after the death of the Pevensies in "our world" during Last Battle and must involve Susan.