A Cauldron is an underground facility where machines are built. By overriding these, Aloy unlocks the ability to control new machines. In Horizon Zero Dawn there are four major Cauldron activities, plus a fifth in Horizon Zero Dawn: The Frozen Wilds.
Project Zero Dawn envisioned a series of underground facilities to rebuild a lifeless Earth. These facilities would be controlled by GAIA while the subfunction HEPHAESTUS would oversee construction of Cauldrons where specialized machines would be designed and constructed for use in terraforming. The inhabitants of the New World are aware of the cauldrons, and some have deduced that they are where machines are built. A few have attempted to venture inside and discover its mysteries, although only one has been successful.
The entrances to cauldrons always feature a triangular structure.
There are five cauldrons in the world of Horizon Zero Dawn. A sixth, Cauldron PSI, is known to exist, although its location remains unknown.
- Cauldron SIGMA : Basic puzzles and Fire Bellowback boss fight
- Cauldron RHO : Moderate puzzles and Snapmaw and Ravager boss fight
- Cauldron XI : Eclipse camp and several machines and cultists as boss fight
- Cauldron ZETA : No puzzles and Thunderjaw boss fight
- Cauldron EPSILON FW Moderate puzzles and Fireclaw boss fight.
- The Cauldrons were designed to be unnatural and alien in appearance.