When designing this environment, I first began with the base inspiration of the main entrance of Howl's Castle where the hearth lay, as I wanted to create an environment with industrilal/steampunk aesthetic, and much of Ghibli's work has elements akin to that..
After deciding on a mages' atelier and then remembering how all manner of things tend to be crammed around or hanging from the ceiling in similar depictions, I began trying to fill in the design to the brim with rugs hanging from the pipes like clothes on a line and lanterns to light the dark chamber..
The furnace acting as the centerpiece I based on old oil lamps, and the chairs attached to the walls were inspired by the student desks seen in the orphanage in Made in Abyss.