You know a building complex is big when it has its own internal rail system. This steel mill complex has standard gauge tracks inside it on the right, but also a 24" network up on the warehouse floor.

I can't recall seeing any of the small locos, unfortunately. It's entirely possible they once had "fireless cookers", small locomotives powered from an insulated tank refilled with steam/water from the mill's boilers. That way there was no smoke in the building, and very little fire hazard.

I know Mesta Machine in Pittsburgh had a two-mile-long shop that was full of fireless cookers as late as 1970.