This guide will show you how to complete the Deep Secrets of the Earth, a main quest in Horizon Zero Dawn. Read on to learn the objectives, strategies, location, and rewards for the Deep Secrets of the Earth main quest.

Deep Secrets of the Earth Quest Information

General Info

Warning: This quest will immediately trigger the next main quest, The Terror of the Sun. There will be a difficult fight during that mission, so make sure to prepare before descending into the ruins at Step 5.

Deep Secrets of the Earth Walkthrough

How to Complete

	Objectives
1	Go to Sunfall. The site for Project: Zero Dawn is located under the capital of the Shadow Carja. Head over to Sunfall, located to the northwest of the world map.
2	Go to the Citadel Courtyard. Head up to the courtyard to test whether the Shadow Carja communication network is down. Use the Campfire to save before going any further.
3	Enter the Citadel. Enter the citadel, following the mercenaries as they are briefed on a new bounty. It is here that you will also receive the Traitor's Bounty side quest.
4	Go to the Grand Balcony and Climb Down. Sylens will tell you the way down is by the broken balustrade in the Grand Balcony. Go to the area behind the throne room and look left. Climb down to the lower levels using the marked path.
5	Use the Secret Entrance. Use Sylen's secret entrance to get to the underside of the Citadel. A cutscene will play showing Aloy bypassing the large door.
6	Explore the Project: Zero Dawn facility. Head further into the Project: Zero Dawn facility, following the waypoints as you go.
7	Enter the Viewing Room (Gen. Herres' Message). Enter the viewing room and listen to General Herres' message regarding the truth behind Operation Enduring Victory.
8	Kill or Evade the Shadow Carja. In the room after the first viewing room will be 3 Shadow Carja. Climb the ladder to your immediate right and use the catwalks to evade the enemies. Drop down to the 2nd Viewing Room entrance and proceed.
9	Enter the Viewing Room (Dr. Sobeck's Message). Enter the viewing room and listen to Dr. Sobeck explain what Project: Zero Dawn is.
10	Kill the Shadow Carja in the Processing Area. Follow the waypoints after exiting the viewing room. After a few doors, 3 Elite Shadow Carja with Firestrikers will appear at the end of the hallway. Kill them to proceed.
11	Restore Power to the Door. The door leading into the Central Projects is locked and you'll need to restore power to it. Head over to the corridor to the right (facing the locked door) and find 2 sets of Holo Locks you have to solve.
12	Unlock the 1st Set of Holo Locks. The first set of Holo Locks is the one without the missing emitter. Solve it by scanning the Code Nexus and matching the pattern displayed. From left to right, the solution is as follows: West, North, West, South, East.
13	Retrieve the Emitter. The first set of locks opens the Supply Room door. Head inside and climb to the second floor. Grab the emitter and drop back down to the Holo Lock room.
14	Insert the Emitter into the 2nd set of Holo Locks. Insert the missing emitter to power up the 2nd set of Holo Locks. Scan the Datapoint beside the Code Nexus to know that the nexus was installed upside down.
15	Unlock the 2nd Set of Holo Locks. The solution to this set is as follows (from left to right): South, West, North, East, South.
16	Open Door and Enter the Central Projects Room. With the 2nd set of Holo Locks done, head back to the original locked door and head into Central Projects.
17	Kill the Eclipse. There will be multiple Eclipse soldiers waiting for you inside. Deal with them and make your way through the different project rooms.
18	Find the Entrance to Sobeck's Office. Follow the waypoints to reach the entrance to Sobeck's Office. Use your spear to pry open the busted door.
19	Examine Elisabet Sobeck's Terminal. Examine and download information from Sobeck's Terminal. Once finished, Helis (the Eclipse leader who killed Rost) will appear and capture Aloy.
20	Trigger the next Main Quest. This step is automatic and inevitable. After Helis finds you inside the Zero Dawn facility, he will knock you out and trigger the main quest, The Terror of the Sun.

Tips and Strategies

Prepare for The Terror of the Sun Quest

At the end of this quest, the main quest The Terror of the Sun will automatically trigger. Players will face a difficult enemy during this mission so make sure to buy upgraded armor and weapons before proceeding with Step 5.

Consider buying the Shadow Hunter Bow or a Shadow Ropecaster if you have not done so. Additionally, the Shadow Carja merchant in the citadel sells the Golden Fast Travel Pack which allows for unlimited Fast Travel.

Evade the Shadow Carja when Possible

Visibility inside the bunker will be very poor and cover during fights will be a bit janky. When possible, avoid enemies or use stealth takedowns to prevent fights from breaking out into open combat.

Use a Blast Sling or Sharpshot Bow to Kill Humans

The Shadow Carja soldiers will be very hard to kill during this level due to their large HP pools. Use a Blast Sling with damage modifiers to make quick work of the grunts if you have the weapon.

Alternatively, Precision Arrows fired from a Sharpshot Bow deal high impact damage. This is perfect for hitting those high-damage headshots on human enemies.

Horizon Zero Dawn Quests

List of Main Quest Guides

Main Quest Guides

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