Wild thoughts ran through me.
On what mischief was the young fiend bent now?
Then he laughed low to himself; then he turned his face to the wall, took a step in my direction, and, to my surprise, began to climb down the wall.

In an instant I saw that there must be steps in the wall; it was plain.

They were cut into or affixed to the wall, at intervals of about eighteen inches.

Rupert set his foot on the lower one.

Then he placed his sword between his teeth, turned round, and noiselessly let himself into the water.