Deep Secrets of the Earth is the seventeenth main quest in Horizon Zero Dawn. KEY NOTE: The ensuing storyline dialogue you will encounter in this mission can be increased/altered by completing several side missions and the Frozen Wilds expansion pack first, before prying open the wood panel covering the vent (the part where Sylens informs you it is a point of no return). Fully completing each of the following is known to create distinct changes:
- The entire Frozen Wilds expansion campaign
- The sidequest Traitor's Bounty
- The sidequest Queen's Gambit
After successfully infiltrating the Eclipse base and taking down their Focus network, Aloy makes her way to Sunfall, the Shadow Carja capital, where she hopes to find more answers about Elisabet Sobeck and Project Zero Dawn.
Entering the city, Aloy looks down from a balcony into the Sun-Ring where a number of Shadow Carja soldiers are attempting to handle a Behemoth. Sylens welcomes Aloy to the Citadel. In the courtyard, Aloy is ushered into the throne room along with a crowd of mercenaries who have gathered to hear High Priest Bahavas announce the day's bounties. As Bahavas announces a bounty on a man named Uthid, a woman approaches Aloy in the crowd, telling her that she wishes to meet with her in Shadowside. As the woman takes her leave, Sylens informs Aloy that the entrance into the Old Ones facility is behind her.
Scaling the rock formations, Aloy finds a covered vent on the other side of a tower. Entering through the vent and descending deeper into the earth, Aloy comes to the door of the facility. While her genetic identity is confirmed and access is authorized, there is a malfunction that bars the doors from opening. She authorizes an emergency venting procedure and the doors open, but a loud mechanical noise alerts the Shadow Carja Kestrels to something amiss in the ruin.
With little time to explore, Aloy begins exploring the Project: Zero Dawn facility. She enters a holographic theater and a message from General Herres of the Old Ones' U.S. Robot Command explains the true purpose of Operation: Enduring Victory. He reveals that Zero Dawn was not a top-secret superweapon program that would save humanity, as it was purported to be. In reality, the Faro Plague had become too advanced for it to be stopped, and the extinction of all life on Earth was inevitable. Operation: Enduring Victory was implemented purely to buy time for Elisabet Sobeck and her team to finish Project: Zero Dawn.
Continuing on to the next room, Aloy discovers that some Kestrels have entered the facility. After killing them and scanning the datapoints, Aloy continues on to find another theater with a hologram message left by Elisabet Sobeck who finally explains what Project: Zero Dawn is: a terraforming system controlled by an artificial intelligence unit called GAIA. Through GAIA and her sub-functions, the artificial intelligence would shut down the FARO robots and eventually reform the earth to re-create humanity. Aloy takes out more Kestrels and restores power to an ancient door to reach Central Projects.
After killing the waves of cultists that descend into the room, she heads for the second floor. As she passes through the vast rooms she is introduced to a few sub-functions of GAIA, learning their functions through holographic messages left by the Old Ones. She eventually comes to a room where Travis Tate explains the purpose of HADES; a failsafe system that would seize control of the terraforming system in the event that GAIA produced a world that was unsustainable or uninhabitable, deconstructing the world so that GAIA may try again. After learning about ELEUTHIA from a hologram of Patrick Brochard-Klein, Aloy deduces that All-Mother mountain must be one of the Cradles created to produce humans.
Climbing up the elevator shaft, Aloy comes to a room with a number of datapoints containing interactions between Elisabet and an early GAIA as well as Ted Faro. Prying open the door to Sobeck's office, Aloy finds and copies the Alpha Registry master file that will allow her access to the facility in All-Mother mountain. As Aloy and Sylens argue about her origins, more Kestrels descend outside the office, including Helis who throws a blast bomb. The explosion stuns Aloy, allowing Helis to approach her and knock her unconscious.
Some time later, Aloy awakens to find herself unarmed and unarmored, suspended in a cage above the Sun-Ring. Helis approaches, telling her that before she crashed the Eclipse network, he sent an order out to rally the Eclipse to invade the Sacred Lands. He then destroys her Focus. Now addressing the crowd, two Corruptors enter the Sun-Ring and begin corrupting a restrained Behemoth. Condemning Aloy to be the first of thousands to die, she is dropped into the Sun-Ring to face off against the machine.
- Go to Sunfall
- Go to the Citadel Courtyard
- Enter the Citadel
- Go to the Grand Balcony
- Climb down
- Use the Secret Entrance
- Explore the Project: Zero Dawn facility
- Enter Viewing Room
- Kill the Shadow Carja
- Enter Viewing Room
- Go to Processing
- Go to Central Projects
- Restore Power to The Door
- Enter Central Projects
- Kill the Eclipse
- Find the Entrance to Sobeck's Office
- Examine Elisabet Sobeck's Terminal
The following datapoints are obtained automatically during this quest and cannot be missed.
- #10 The Bad News
- #11 The Good News
- #12 Gaia Log: 27 March 2065
- #13 Gaia Log: 5 June 2065
- #14 Gaia Log: 13 January 2066
Text Datapoints - Quest
- #40 Sobeck Journal, 11-19-64
- #41 Sobeck Journal, 7-16-65
- #42 Sobeck Journal, 10-31-65
- #43 Sobeck Journal, 1-15-66
- #44 Gaia Log: 3 Feb 2065
- If Traitor's Bounty and Queen's Gambit are completed before this quest, Helis will comment on the death of Bahavas and disappearance of Itamen and Nasadi.
- Aloy will mention seeing "Stalkers. Ravagers. A Thunderjaw" in Cauldrons, even if the player has not completed such Cauldrons yet.