This quick tour of subterranean spaces--caves to badger setts, sewers to subways--features simplified cross-sections scattered with rocks, tree roots, bones, rubbish, small cartoon figures, and captions of one or two sentences. To give readers a little context for what they're seeing, Kent (Go to Jail!, p. 340, etc.) heads each topical spread (""Homes,"" ""The Street Beneath Our Feet,"" etc.) with a paragraph of introductory remarks, and includes diverting historical anecdotes in sidebars. Although the sewers and dungeons depicted are suspiciously clean and well-lighted, children who find the art of Stephen Biesty too busy to follow will enjoy these more orderly visual excursions.