I got this structure from Shereen LaPlantz' "Cover to Cover," the first book on bookmaking I ever owned. It's really quite simple. You just fold your long long strip of paper in a triangle, then a straight fold, then another triangle in the other direction, then another straight fold, etc. It's very similar to folding up a flag, if you've ever done that. The covers are mat board covered in a decorative Japanese paper. Ribbons are glued between the covers and the end papers, then the folded accordion is glued onto the insides of the two covers. Tie it up and you're done.
One point LaPlantz makes--and I can verify it from personal experience--is that when you are making these kinds of folded books it is crucial to be very exact with your folds. Points must be perfect, lines all straight. A really small error in the folding will compound rapidly and throw the whole thing off by the time you're done. Ask me how I know!
I've been poring over bookmaking books the last few days and I'm getting very anxious to start making some more complicated structures, some that will take more than a day. What I will likely do is have a few going at a time so that I can finish one every day for posting. I think that's kosher for the challenge.