It consisted of building anew his air castle, and in riding out to the forbidden lava ridge that rose like a wall out of the sandy plain west of Sinkhole to choose the niche which might best be converted into a secret hangar.
Since first he heard of the derelict airplane, his mind had several times strayed toward those deep clefts, but his feet had heretofore refrained from following his thoughts.
Niches there were many, but they were too prone to yawn wide-mouthed at the world so that whatever treasure they might have contained would be revealed to any chance passer-by.

These Johnny disdained without a second glance.

Others he investigated by riding in a little way, sending a glance around and riding out again.
Just before dusk, as he was returning disappointedly after looking as far as was practicable, his horse Sandy swung into one of the open-mouthed depressions of his own accord.

Probably he had become convinced that they were hunting stock, and that every niche must be entered.

(Range horses are quick to form opinions of that sort and to act upon them.) Johnny was dreaming along, and let Sandy go back toward the wall, but Sandy, poking along with his head bobbing contentedly at the end of his long neck, swerved to the right, into a nature-built ell that had a fine-sifted sand floor, walls that converged toward the top, and an entrance which no one would suspect, surely, since Johnny himself had passed it by not half an hour before.
Johnny did not say a word.