Great Furnace

The Great Furnace is the location of the Subrosian ore-smelting forge in. According to the Subrosians working in the forge, the furnaces are capable of melting any metal. On Link's adventures, it is used to smelt Red and Blue Ore into Hard Ore, which is needed to create the Iron Shield (or the Mirror Shield, if the former has already been obtained via Linked Game).

Overview
The Great Furnace is located directly northeast of the Sign-Loving Subrosian's home and north of Lava Lake on the eastern edge of Subrosia. The exterior of the building is accoutered with the furnace's ventilation systems and hydraulic equipment. Inside the building, a pool of lava stretches the length of the forge's west wall. Another smaller pool can be found near the entrance. It is assumed that the heat of the lava is harnessed to make the furnace function. The furnace itself appears to be shaped like a face (not unlike the entrance to the Sword & Shield Maze), with a blazing oven for a mouth.

Operations in the Great Furnace are overseen by the Subrosian Smelter. Four other Subrosians work at the furnace.

Trivia

 * Some superstition appears to be involved in the Subrosian manner of smelting metal, as the smelters can be seen performing a dance in front of the furnace while the ore is being smelted.