Big Busy Building

``Busy'' doesn't begin to describe the multitudinous characters and scenarios in this upbeat tour of the eponymous edifice. With its appropriately tall, narrow shape (and kid-proof, board-book stock), this wordless book teems with fun on each of its five chockablock spreads--and on front and back covers as well. Every setting on every floor demands close scrutiny, and rewards youngsters with an abundance of details both absorbing and amusing. From the industrious mice who revel in their basement habitat (and show up in comically unexpected spots throughout the building) to the assorted residents of the imaginatively used (and die-cut) gable space, characters are glimpsed in a plethora of pursuits. A poodle awaits a do in a beauty parlor; a human baby and a baby porker bide their time in a doctor's waiting room (the piglet later runs amok in other establishments); a girl buys a fish in an aquarium shop. An especially energizing feature is a small plastic elevator: embedded on the last page and visible through a vertical cutout on each preceding spread, it can be slid up and down the building's height. An architectural gem. Ages 3-up. (Apr.)