Secret openings can be concealed within a fireplace, a wall bookcase unit, cupboard or cabinet. The secret, one expert argues, is to use the "dead" space in a home. Whether it's a passageway underneath a staircase or a doorway that leads to space originally designated as part of a furnace room, closet or crawl space, Steve Humble, president and founder of the decade-old Creative Home Engineering firm, based in Gilbert, Ariz., says the key to having a secret room is that visitors don't even know one exists within the home.