used to go between levels so a flat escalator, can take trolleys or there is a trolley chain haul beside. Bunnings (Hammerbarn if you must) have them. Giant tilt slab constructed category killers. Where sprawl is permitted they're a one layer building but in space constrained areas they have two or three (carpark under a 2 layer building) and these walkways exist to get your inflatable shark, chainsaw and bucket of chips down or up, depending.