We always have a box of paper towel tubes around. I save them for different homeschool preschool projects. This paper towel tube project is a simple tunnel marble run. You can, of course, make it as complicated as you wish, attaching paper towel tubes at different heights so that the marble jumps from one to the other, etc.. We did a really simple tunnel. Our goal was to position the basket ( or the plastic box in our case) correctly, so that the marble jumps right in it. We used duct tape to attach the tubes.