Then she deliberated.

If she went around to the front so as to get access to the steps, she might pass in range of the loiterer whom she mistrusted.

That risk she would not incur.
Examining the wall that enclosed the box-like stairway as best she could in the dark, she found it rickety, full of holes and cracks, and she decided she would climb it.

A sheer perpendicular board wall, some twelve or fifteen feet high, shrouded in pitchy darkness and apparently within earshot of a police spy, did not daunt Bessy Bell.
Slipping her strong fingers in crevices and her slim toes in cracks, she climbed up and up, till she got hold of the railing post on the first platform.

Here she had great difficulty to keep from falling, but lifting and squirming her supple body, by a desperate effort she got her knees on the platform, and then pulled herself to safety.