This report documents the forty-third confirmed occurrence of unexplained footprints appearing in freshly poured concrete at construction sites in the Shelf district. The footprints are always bare feet. They are always the same size: 24.1 centimeters in length, consistent with a human foot of approximately women's size 7 or men's size 5.5. They are always left in concrete that was poured within the preceding ten minutes. They are always found when the pour site was under continuous surveillance with no human presence.

The first occurrence was recorded in 2196 during the reconstruction of a residential stairwell on Shelf Tier 3. The construction foreman, Abiodun Chaudhary, poured the landing slab at 06:40, sealed the site, and returned at 06:55 to check the set. Seven footprints crossed the slab in a straight line from the south edge to the north wall, where they stopped. Not faded — stopped. As if the walker had stepped into the wall. Surveillance footage from the site's security camera shows the slab surface deforming in sequence over a period of twelve seconds. Nothing is visible above the surface. The impressions appear as if pressed by weight, but no weight is present.

The footprints have since appeared at twenty-nine different construction sites across the Shelf, always in fresh concrete, always the same foot size, always barefoot, always when no one is present. The stride length is consistent at 58 centimeters — a short, unhurried step. The depth of impression suggests a body weight of approximately 52 kilograms. The gait analysis indicates a slight leftward lean, as if the walker favors their right leg. We know the walker's shoe size, weight, stride, and gait. We do not know who they are. We do not know what they are. We do not know where they go when they walk into walls.

Construction crews in the Shelf have developed a practice of leaving a section of each new pour uncovered as an offering of sorts — a place for the walker to step without ruining structural concrete. The practice is unauthorized and I should be discouraging it. I am not discouraging it. The footprints have not appeared in any structural element since the practice began. Whatever is walking through the Shelf is polite enough to use the path we leave for it.