From Destinypedia, the Destiny wiki
The Hellmouth is a location on the Moon that refers to both an underground fortress constructed by the Hive and the area of the Moon's surface surrounding the massive pit that gives the fortress its name. It serves as the main staging ground for the Hive god Crota and his forces for their invasion of Earth. The Hellmouth features an inner sanctum, gatehouse, and dungeons that are located in the depths of the fortress, imprisoning the Hive's most fearsome denizens.
The Hellmouth's many underground passages reach far and deep into the Moon; besides the main entrance through the Gatehouse, it also has tunnels connected to the Temple of Crota and Archer's Line. Within the Hellmouth itself is a labyrinth of chambers for various purposes; The World's Grave, containing the Hive's collective history and many of their secrets, the Chamber of Night, where the Hive perform profane rituals, the Summoning Pits where Phogoth is kept chained, the Shrine of Oryx where the Hive contact their mighty king, Oryx. In the deepest, darkest pit in the Hellmouth is a rupture leading to the Oversoul Throne, the throne world of Crota, Son of Oryx.
Two years after the Red War, the Hellmouth is still a prominent Hive Stronghold on the moon, now entirely under the guard of the Hidden Swarm instead of the Spawn of Crota. Parts of Hellmouth's structure seem to have been stripped apart, presumably to construct the Scarlet Keep.
Points of interest
The outer surface of the Hellmouth covers a wide area, including a platform overlooking the pit and a small moonbase hidden away in the rocks. Public Events, resource nodes, and patrol beacons can only be found on the surface of the Hellmouth, not within.
List of appearances