What's inside a hill? What's behind the walls of a house? Where is the underground home of the mole? What's it like inside a lighthouse? Inside a wasp's nest? Inside an egg? Under deep water? Simple explanations of unseen wonders of everyday, well done in understandable text and diagram-like drawings in 3 colors. But it is a difficult book to use with just any child, as there is no real focus of thought; and the interest levels are so different that the whole seems a bit haphazard.