What is the last torture in The Pit and the Pendulum that the narrator faces?

After he slides off the board, the pendulum stops swinging, and, the narrator says, "I beheld it drawn up, by some invisible force, through the ceiling." Apparently, he concludes, someone has been watching him. Did he escape the pendulum only to be subjected to another form of torture?

.......At that moment, he notices that the sulfurous light in the cell is coming through a fissure running around the base of the walls. He also notices that the images on the wall are now staring at him with fiery demonic eyes and that the smell of hot metal has invaded the cell. It is the iron walls; they are heating up.