I just read, or rather, just looked at The Line by Paula Bossio. With no text at all, this book tells a wonderful story of a little girl and her exploration of a line she finds. It can be a slide, she can hang from it like a set of monkey bars, do anything she likes. But where has it come from and where is it going? How will it end? We are following along with her to find the answers to these questions.
This is a wonderful book for encouraging kids to use their imaginations. Since it's wordless, they can imagine what is going on in the girl's mind. They could write their own story to accompany the pictures. I've used Harold and the Purple Crayon for years to show students how lines and shapes can convey a sense of movement or emotion. This would work perfectly for that, too. They might even like to draw the activities they would try if they were in the story.
You can see a preview of some of the pages at the publisher's website.