100 Cupboards — N.D. Wilson

Lying in bed at night, twelve-year-old Henry York can't ignore the thumping and scratching he hears on the other side of the attic wall. He scrapes off the plaster and discovers doors -- ninety-nine cupboards of all different sizes and shapes. Through one he hears the sound of falling rain. Through another he sees a glowing room -- with a man strolling back and forth! Henry and his cousin Henrietta soon understand that these are not just cupboards. They are, in fact, portals to other worlds.