The Great Furnace is a location from The Legend of Zelda: Oracle of Seasons. Located in the subterranean country of Subrosia, it is situated just west of the Sign-Loving Subrosian's house and north of Lava Lake. The Great Furnace is home to Subrosia's ore-smelting furnace.
After taking the Bomb Flower to the Temple of Seasons, the two Subrosians who run the furnace return to it and tell Link to visit them whenever he needs ore melted. Upon returning with the Red and Blue Ores, they will use the furnace to combine the two into an alloy of Hard Ore, which can then be used to forge the Iron Shield.