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"The lesson will be taught in due time, Aloy. Until then, we wait."
This article contains heavy spoilers, and may reveal plot or quest information.

Cauldron EPSILON is a location in Horizon Zero Dawn: The Frozen Wilds, located within the 21st century facility known as Firebreak. Before its destruction, it was located at the very back of Firebreak's Battery Facility, and served as the manufacturing facility for the daemonic machines found within the Banuk region known as The Cut. It was also a research and development facility where its creator and overseer, the artificial intelligence HEPHAESTUS, embarked on a drive to develop hunter-killer machines to hunt and kill humans.


Like the five known Zero Dawn cauldrons, the design of Cauldron EPSILON heavily features geometric patterns, especially triangles. However, as the first cauldron designed solely by HEPHAESTUS, it differed from the Zero Dawn cauldrons in a number of respects. Firstly, as the cauldron was built over the preexisting Firebreak facility and parts of an active (albeit controlled) volcano, Firebreak components make up a noticeable part of EPSILON's infrastructure, and parts of the volcano have been left untouched in the construction. Secondly, rather than the pale blue lighting of other cauldrons, the lighting is a deep purple. Thirdly, the compromised parts of Firebreak are surrounded by purple wiring, reminiscent of a parasite. Fourthly, it is the largest cauldron by far, and the most heavily guarded. The fifth and most important difference is that unlike the five known Zero Dawn cauldrons, HEPHAESTUS “personally” oversaw EPSILON’s operations.


Cauldron EPSILON was built by HEPHAESTUS, a former subordinate function of the Zero Dawn terraforming system's governing AI GAIA. Having chosen the location due to the natural geothermal energy and mineral resources available from the magma that the facility tapped into, HEPHAESTUS commandeered the Firebreak facility, enslaved its governing AI CYAN, and built the cauldron. There it set about developing even more aggressive and dangerous machines, including commencing research and development of hunter-killer units to eliminate humans.

However, its actions against CYAN drew the attention of a Banuk shaman named Ourea, who had formed a strong bond of friendship with the AI before HEPHAESTUS enslaved it. This culminated in her forming an expedition consisting of herself, her brother Aratak, erstwhile chieftain of their werak, and the Nora Brave Aloy. Led by Aloy, the party successfully infiltrated the cauldron. Ourea overrode its core, albeit at the cost of her life, freeing CYAN. CYAN caused the cauldron to self-destruct, foiling HEPHAESTUS' plans, at least temporarily.

EPSILON Overrides



Frozen Wilds Audio Datapoints

Frozen Wilds Text Datapoints - Quests


  • The Cauldron is located slightly outside of the game map.
  • Upon completion of The Forge of Winter, the cauldron is destroyed. As such, its access door is permanently sealed on subsequent visits to the Firebreak facility.