noun
ledge
LEJ/ledʒ/
A narrow shelf or ridge projecting from a surface.
A narrow stone ledge projects from the steep rock face.

Etymology
Ledge first meant a crossbar on a door, before acquiring the sense of a narrow shelf or shelf-like rock projection. Its origin remains uncertain.
In context
a regular succession of footsteps in the dust along the ledge, between one window and the other.