Authors build elaborate worlds through everything from carefully-chosen foods to amateur map-making to breathtakingly detailed wikis, their attention to detail a signal that these are worlds worthy of getting lost in. Often these are specific moments in the text, or a helpful hand-drawn atlas bookending the epic adventure, or a bonus feature that’s just a click away. But some storytellers go the extra mile, embedding worldbuilding details into their texts as a sort of “found footage”—fictional childhood stories, comic books, or newspaper clippings that appear as excerpts throughout the larger work. Sometimes, these fictions-within-fictions take on a life of their own and emerge into the real world as self-contained stories in their own right. Crack a book, cross a bridge, hop a spaceship, and check out these eight stories that are wonderfully extra when it comes to worldbuilding, creating children’s stories that can hold up to the classics, spinning off into picture books drawn from your nightmares, or even spawning entirely new book franchises. You know, like you do.