Uontau, like Imo Caecae, is a mythical underworld. The Uontau is a harsh hell where all evil beings go to die. Uontau is ruled by Rez. Uontau does have a counterpart, Yiyata, which is also ruled by Rez but is the graveyard of good spirits.
Uonz is the Olympian word for evil, while tau means grave or graveyard.
Uontau is an endless plane filled with volcanic craters, pits, trenches, and geysers. Most of Uontau's inhabitants are spirits of the dead who are endlessly punished by Demonicans, demonic servents of Rez. The Demonicans make sure all the spirts stay in Uontau; ones who attempt to escape are sent to Rez for severe punishment.