100 Cupboards (100 Cupboards #1) by N.D. Wilson

Twelve-year-old Henry York is going to sleep one night when he hears a bump on the attic wall above his head. It's an unfamiliar house—Henry is staying with his aunt, uncle, and three cousins—so he tries to ignore it. But the next night he wakes up with bits of plaster in his hair. Two knobs have broken through the wall, and one of them is slowly turning...

Henry scrapes the plaster off the wall and discovers doors—ninety-nine cupboards of all different sizes and shapes. Through one he can hear 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.

100 Cupboards is the first book of a new fantasy adventure, written in the best world-hopping tradition and reinvented in N.D Wilson's own inimitable style.