Cerberus' Lair is a dungeon that borders between the River of Souls and the rest of RuneScape. It is inhabited by Cerberus, a three-headed hellhound, who guards the River of Souls, preventing the living from entering, and the dead from escaping. The lair is also inhabited by the Key Master, who is tasked with preventing Cerberus from escaping the iron gates that hold it.
The lair may be accessed via a cave entrance in the north-eastern section of the hellhound area within the Taverley Dungeon. This leads to the Key Master, who guards three iron gates that lead to Cerberus. He will only allow players who are assigned hellhounds or Cerberus as a slayer task to fight it.
The player speaks to the Key Master.