The Fireheart takes the form of a great spherical fortress of scorched stone surrounding an gigantic empty core, where the god of rage Malvar is imprisoned. It is said to exist in the core of the world.
In the inner sphere of this realm the god of rage constantly fights for freedom from the chains of Malvarite that hold him. He tries his best to use all of his adrenaline and rage to try to loosen the chains, while the Firehearted and the Hounds of Rage try to suppress his movements. There is no air inside this sphere only the god's orange sweat that has characteristics of both air and water. This allows for fighting in a 3D environment, but is extremely hot and might hurt the lungs of those that breathe it.
In the fortress lies a confusing barracks maze filled with Firehearted. Some of them can be found fastening the chains that bind their god, while others train to fight a arm or leg of the god in case it ever gets lose. The Hounds of Rage either fight to restrain the god or to free him in this fortress. Malvarite ore and Rage Adrenaline can be found plastered on the fortress walls.