The Nether Spire was completely made out of Netherrack (formerly Obsidian due to Netherrack being unimplemented). After the Nether Reactor's "energy" ran out, the Spire became damaged with several holes that allowed the player to exit the area, and the time would fast-forward to Night. The floor above the reactor contained an area where Mob Farming could be performed. If the player could make it to a higher place of the Spire, it could be climbed. This was the only legitimate way to get Netherrack in survival mode. If the Nether Reactor Core was broken before mob/item spawning was finished, the Nether Spire would not break.