The cover of The House With a Clock In Its Walls, by John Bellairs and illustrated by Edward Gorey. A silhouette of a Victorian mansion looms over a small boy, with a ghostly face surrounded by clock numbers imposed over it.
I recently reread this childhood treasure--
"From deep within the tomb came a sound. Boom! A deep hollow sound. The iron doors jolted, as if they had been struck a blow from inside. The chain rattled, and there was a clunk on the pavement. The padlock had fallen off..."