L. Frank Baum

“ Miguel or Arthur pushed hard against every block in the room, from those nearest the floor to those far above their heads; but not one yielded a hair’s breadth.
“Suppose we go outside,” said Patsy. “Perhaps there is some window, or grating, that will give us a clue.”
So they took old Miguel’s lantern and went into the garden where they could view the outer side of the wall. A tangle of climbing vines grew against the wing, but there was no window or other opening on the first floor. Above, on the second floor, were two windows, one of which admitted light and air to the blue room. ”

“ Old Miguel had been silent and unobtrusive in the vacant room, but here he was as eager in testing the wall as any one of them.
“You see, it’s this way,” Patsy was saying; “if the major could hear baby cry, through this wall, those inside could hear us, if we called to them. Who among us has the clearest, the most penetrating voice?” ”

“ It was Patsy who questioned him. He mused a bit before replying.
“The old señor—the father of my Señor Cristoval—was strange mans,” said he. “He make thees house a funny way. Come; I show you.”
He led the way to the little room adjoining, the one Inez had occupied. In one corner of the floor was a square hole, with steps leading down to a sort of blind pocket. Holding a lamp in one hand Miguel descended the steps and pushed against a block of adobe that formed part of the outer wall. ”