This chapter contains a complete walkthrough for the quest Deep Secrets of the Earth. Here you will find advice that will help you to complete the quest in the best way possible.
The quest will appear in the journal directly after completing the mission To Curse the Darkness. Go to the Sunfall in order to start this mission. Once you get close to the city, Sylens will contact you again. Use the main entrance to the Sunfall to go directly to the Citadel.
Join the group of bounty hunters and follow them. After the cutscene you must go towards the arena. Now you must walk to the lower floors, to the entrance to the ruins. Use the hole in the fence shown on the above picture to get lower.
Inside you will find plenty of recordings and new chambers. At some point you will reach the room with a hologram. Behind it there is another one, this time with a few Carja warriors. You will learn that they used the ventilation shaft to get down. Defeat them, listen to new interviews and move forward.
Further you will find new rooms with recordings and cutscenes. Then you will encounter some new warriors. Each of them will have a heavy weapon. You should stand behind the door that leads to the chamber shown above. It is best to set the enemies on fire by putting a few arrows on the bow. You can also use other elemental arrows, but the fire is most effective.
Once the fight ends, you will notice that the next door isn't powered. Use the stairs on the right to reach the generator room. There you must set the switches in correct way.
The first panel (the only active one) from the generator: left, up, left, down, right.
As you probably noticed, the second panel isn't available. To activate it you must obtain an emitter. After setting the switches in the first panel in correct way you must walk to the door found in the nearby room. Now you should be able to open it. Climb the ladder to the higher floor. There you will find the component. Get back to the console with it.
Before you act, listen to the message located near the panels. You can notice that the Faro writing on the wall is turned around. This means that you must read all the arrows backwards, as it was mentioned in the recording.
The second panel: down, left, up, right, down.
Go back to the door after activating both panels. Now you should easily pass through them. On the other side you will encounter a group of cultists. The best way to get rid of them is to set them on fire. Hide behind pillars and dodge. There is a small chance that one of the enemies will get close to you. Once you eliminate the first group, another one will appear. This time there will be much less enemies, but two of them will use machine guns. Burn them one after another or kill one of them and them take down the rest with the machine gun.
Then follow the marker to reach Sobeck's office. There you will find another group of cultists. The principle is the same - set them on fire and hide behind cover. Kill them all. Look for some new recordings and notes. Once you're done, go to higher floor.
There, behind the blocked door you will find Sobeck's office. Look for some more recordings and interact with the terminal.
A long cutscene will start. The mission will end and another one will be added to the journal - The Terror of the Sun.