Tillie and the Wall by Leo Lionni
For as long as the mice remember, there has been a wall. No one could see beyond the wall, it was too tall and too long. The mice never questioned what was on the other side; they mostly forgot that the wall even existed. That, is, until Tillie became curious. She tried everything she could to see beyond the wall until she dug a big hole under it. What Tillie found made her a hero to the mice.
Once again, Leo Lionni does not fail. His collage illustrations along with this creative story are perfect for the young reader (along with the old!) This tale is timeless. It inspires the reader to think outside of the box (or the wall). I would highly recommend Tillie and the Wall.