Hellmouth

An enormous fortress in the Underworld


 * It is ringed with walls of Iron.
 * Its only entrance is a gate of an iron-fanged beast with three eyes.
 * Comment: Could be Deshkorgos


 * It lies within the Swamp of Despair
 * Through the Hellmouth is the Pit of Vakalta

Source: Sartar: Kingdom of Heroes, Eleven Lights