The forge is an important structure that provides the player the ability, for the first time, to smith metal tools, particularly iron and steel, and is likewise an early milestone for the developing tribe. It contains a central furnace which can be lit with a fire starting tool and burns forever unless manually extinguished. Because it essentially offers an infinite heat source, it is useful for refining ores and cooking food, though the range at which the furnace can effect nearby items is limited, which may make refining large quantities of materials difficult. This is circumvented later should a player be able to build the vastly improved cousin to the forge, the smeltery, which provides a considerably larger space for smelting and offers a more extensive set of recipes which unlock access to mithril and bluesteel tools.
Before the overhaul to the crafting system through the use of a polished, central UI, the anvil located inside the forge functioned as a 'crafting ingredient' which had to be selected first, followed by the recipe of a tool or item in order to actually produce them. This functionality of course was abstracted out into the various crafting stations we see today.