This chapter contains a complete walkthrough for the quest related to Cauldron XI. Here you will find advice that will help you in completing this mission in best way possible.
Beginning the quest
The mission will appear in your journal once you get close to the Cauldron. The cultists will make it harder for you to get to the core and even the location itself. You must defeat them to complete the quest.
Entrance to the Cauldron
After getting close to the Cauldron you will see a large group of Cultists guarding the entrance to the ruins. Sneak up to the bushes inside the palisade and wait for the enemies to get close to the exploding barrels. Use burning arrows to get rid of most of them, especially the one with a machine gun.
Then search the bodies of the fallen in order to find the key. Go to the top of the scaffolding. There you will find an entrance to the facility. Interact with the gate to continue the mission.
Explore the ruins
After entering the area you must first eliminate two cultists guarding the gate. Then you will have a short walk inside the ruins that will end when you find another enemy group. This time there will be three opponents. Burn them or blow them up with barrels. Then go down the scaffolding and to the further chambers.
Later in the quest you will enter an underground cave filled with cult members. Take the opportunity to shoot them from above. Eliminate all enemies that are in your range. There are many opponents in the chamber and you will have to get close to some of them later, so it is a good idea to reduce their number. Especially since as long as you attack them from above, they will quickly ignore you or won't bother with you at all. Once all enemies in the area are killed, go deeper into the cauldron.
Override the core
Then you will participate in a short walk to the chamber of the Core of the Cauldron. There you will encounter more cultists. First, you should eliminate the enemy with a machine gun. Don't use his weapon for eliminating his allies. Finish them with your own equipment.
Replenish your medical supplies and check the Core chamber. Cultists will attack you after you override the data. Use the nearby scaffoldings to prepare a shooting position. Then take the machine gun there. There will be many opponents and they will have heavy weapons. After defeating the humans you will have to face machines. Being on the scaffolding will provide you with much needed advantage.
You must survive for 2 minutes. Then you can safely move from the Core and to the exit.
Leave the Cauldron
This isn't the end of challenges. Now you must face the Stalker. Focus to find his camouflaged body and try setting him on fire while hiding. Repeat the action until he detects you. Try to destroy the cannon on his back and finish him with a strong melee attack. Once the fight is over, open the door by overriding data and go forward.
In the underground cave you will find more Stalkers. Try luring the machines closer and then hide in the bushes. From there you can easily set them on fire or eliminate with a strong attack. There are a few cultists in the cave as well, but they will be too afraid of the machines to risk a direct battle. After killing the third Stalker you can go towards the exit. Climb on the construction and use the handles on the wall.
On the next floors you will encounter Cultists fighting the machines. Kill them all or wait until they eliminate each other. You should finish them up to obtain additional experience, especially since they aren't focused on you.
Finishing the quest
Finally you will get outside the Cauldron. There you can participate in a battle between the machines and the cultists or you can wait until both sides eliminate each other. You can also immediately use quick travel and go away from the Cauldron.