"If I'd been alone the invisible wall surely would have stumped me." Reaching the entrance they began to mount the stone stairs.

They went up ten stairs and then down five stairs, following a passage cut from the rock.

The stairs were just wide enough for the two girls to walk abreast, arm in arm.

At the bottom of the five stairs the passage turned to the right, and they ascended ten more stairs, only to find at the top of the flight five stairs leading straight down again.

Again the passage turned abruptly, this time to the left, and ten more stairs led upward.
The passage was now quite dark, for they were in the heart of the mountain and all daylight had been shut out by the turns of the passage.