Lake Cocytus is the frozen lake of the ninth circle, where those who have committed treachery against God are punished. The lake itself is formed from the tears of Lucifer himself, and the flapping of his wings keep it frozen. It is here that Dante fights Lucifer at the end of Dante's Inferno, serving as the last boss of the game. In the middle of Lake Cocytus is a reversed pentacle that can show images and can be taken apart.
- In both the game and poem, it is the name of the frozen lake where Lucifer is trapped in from waist down. It is said that the lake was created from his tears he shed from his treachery against God. The lake is kept frozen from the wind produced by his beating wings. Only the souls of those who committed unspeakable treachery against God are imprisoned here with Lucifer.
- In "The Inferno", Dante placed Lucifer in the innermost part of the ninth (deepest) circle of Hell, where he was frozen up to his waist in ice. He was described as having three heads, in which he was gnawing upon history's three greatest traitors: Brutus, Cassius, and Judas Iscariot.
- The player can select Lake Cocytus as an arena in the Trials of St. Lucia DLC.
- In Greek mythology, Cocytus was one of the four rivers of the underworld (though it was never depicted as being frozen). Its name means "lamentation"; the explanation of it being formed by Satan's tears in the Inferno is a possible reference to this.