Ok, you're walking through a gigantic shop, complete with its share of metal chips and grease. Then you walk through a door into... a room made of gleaming stainless steel. Pristine, people through glass windows wearing white bunny suits. It was, er, a surprise. This is the place where they micro-clean the already cleaned items, and then measure how clean they got it. The place looks stunning.
This is the "foyer", on the "dirty" side of the door. We did not enter the clean room area.