In a small room, there is a chest, and some stones stacked, that make it seem climbable.
Since I had frogotten how to access the top of the factory, I tried to walk on those stacked stones, and it let me climb them, and pushed me through the roof, onto the second floor.
Had a similar moment at the same location, but in a bigger room, where stones seem climbable, and pushes you up, but not fully through the roof.
I managed to do it more than once.
Here is a link to a post I made in the No Rest for The Wicked Discord server, under the Wicked-Media section: