I recently finish an accordion book collaboration with a terrific artist, Jani Collins. I mailed her a blank accordion book and she did 2 spreads and started the back side and sent it back to me and I completed it with my two spreads and my additions to the back side. This was a great challenge in the best way possible. It's really like art improv. One person starts the idea off and the other one runs with it.
Here are Jani's two spreads and the back:
Next are my 2 spreads and the back and a couple of views of the opened book.