It's estimated that there are more than 9,000 of these "construction sheds" (another term for scaffolding) installed across the city, enough to stretch nearly 400 miles if they were put end to end. They do the important work of shielding pedestrians from potential falling debris during building construction and renovation projects, but they also shroud large swaths of sidewalk in dark and cloistered tunnels made of an unfortunate jumble of steel poles and plywood.