Doom Eternal’s “The Ancient Gods” DLC brings three new missions to the game, which means many new collectibles to be found. Across these three missions, there are 13 physical Codex pages and three Support Runes to be discovered. This guide will detail the locations of the former.
The Codex is a series of background information on the Doom lore, made available to you through the collection of hidden Codex pages throughout the campaign. The base campaign has 55 to be found, while the first of two DLC packs to be released brings the total up to 68. There are four pages to be found on each of the first two missions, “UAC Atlantica Facility” and “The Blood Swamps”, and five to be collected on the third and final mission, “The Holt”. These can be collected on any difficulty.
UAC Atlantica Facility
Work your way through the level until you reach the area with the door that requires the red keycard inside, in roughly the spot pictured in the map below.
To the right of the red access door is a staircase leading down. Follow these stairs downward to find the first Codex page in plain sight in front of the door.
A bit further into the level, you will come to the very top of the first structure. Use your map to work your way into the curved platform area pictured here.
Before interacting with the switch to begin the platforming section to the next structure, turn to the left to see a staircase upward. Head up these stairs to find the level’s second Codex entry to your right.
Immediately after the platforming section following the last collectible, you will have to clear out a room of enemies, including a very dangerous Arch-Vile. Following this fight, you will have to swing over to another area, landing on some catwalks.
Walk to the end of the lowest catwalk near the door, where you should see a walkway extending out and to the right of the building. Jump up onto this walkway and follow it around the corner to find the Codex page.
A bit further into the level, you will find yourself back inside following some more combat. A picture of the location is provided for good measure, though this location is very hard to miss.
Immediately upon entering the building, you will see a large upward staircase on the left wall. Instead of climbing up it, stick to the right wall and head under it, around to the far side of the room. Tucked into the back left corner will be the final Codex page of this level.
The Blood Swamps
Very shortly into the level, you should reach the area of the map pictured below. In this section, you will have to fight a few waves of enemies, so do so, then swing your way through the large rotating firebars over the swamp water to your left.
Climb up the few platforms ahead of you and do a double-jump and dash to reach the far platform to your right, to the other side of the door below. From here, drop down and pick up the diving suit. Submerge into the water directly in front of you and turn around immediately. Underwater in a small alcove will be the first Codex page of the level.
This second Codex page is a bit more involved and won’t appear for another little while. There is one point in the mission, pictured below, where you will have the option to take either a left or a right path. In the end, you will end up taking both, though do note that this guide assumes you are taking the left path first, as that will ensure that the Codex pages are collected in chronological order.
After a long while, you will eventually come to the area pictured below. This staircase is where you go to proceed through the level and it is leading up to a door that will only open once all the enemies in the area are dealt with. Once it opens, instead of going up it, turn around 180 degrees and submerge into the water in front of you, by the far wall.
Advance through the tunnel into a secret area, where you will encounter an empowered demon. Deal with this enemy and then continue forward. At the far end of the area in plain sight, you will find the second Codex page of the level, across a large gap.
Proceed through the level and pay close attention to your map as you do so. You will come to a section of the level that is pretty heavy on the parkour, and after dealing with the enemies at the end of the parkour section, you should find yourself in the spot pictured below.
Stand atop the circular platform overlooking the swamp. You should see a climbable wall in the distance, which you can reach with a double-jump and dash. Do so to reach it and climb to the top. Make a 180 once you are on top and you should see the Codex page on a platform ahead of you. With two jumps and two dashes, you can reach this collectible.
Once again, continue your playthrough of the level for a short while, until you reach the area seen below on the map. Clear out the enemies here to make your life just a tad bit easier, then turn around and face the point of entry to this area.
The Codex page is located directly above the entrance here. To the left will be a ledge you can jump up to reach, so do so and then jump up to nab the final Codex page of the second level.
A decent ways into the level, you will reach this area, which requires you to knock over a tree on a higher ledge to create a bridge to proceed. You can knock over the tree to get ready, but do not leave yet.
Approach the ledge overlooking the map and look straight down. Hidden away on a platform below will be an immediately visible Codex page. Drop down to grab it and then use the climbable wall behind you to get back up.
Further into the level, you will come to an area with numerous small floating islands, as clearly visible on the map. You are going to want to make your way to the third floating island on the right side of the main path to grab the hard-to-miss Codex page.
Continue on your merry way, until you take a gravity lift up to the upper floor of the building, to the area pictured in the map below. Once up here, look to the right and you should see a large door at the end of the bridge, up a ramp.
Head through it to find the third Codex page waiting for you on the left side of the room, in plain sight.
A bit later, after swinging across a chasm and punching through a destructible wall, you should find yourself at the place on the map as seen below. Regularly check your map so you know when you are coming up on it.
Once you land in the room (as seen in the first pictured below), immediately make a 180 and shoot the red target above the chasm a few times. This will unlock the door on the opposite end of the chasm.
Use jumps and dashes to reach the platform to the left of the chasm where you started, then jump over to the opposite side of the chasm from where you shot the target. The previously-locked door will now open, revealing the Codex page.
The final Codex page is right where you shot the target from. Swing back across the chasm and back into the large room. Head to the back right corner to find the final Codex page of the DLC tucked away.
With all 13 of the DLC Codex pages collected, you should unlock your well-earned “Required Reading” achievement or trophy and should be much better understanding of Doom Eternal’s lore.
MORE: The Doom Eternal Horde Mode Mod Is Out Now
- Doom Eternal
- Xbox One
- Xbox Series X
Gavin Burtt is a news, guide and list writer for TheGamer based up north in Ontario, Canada. Gavin has worked as a walkthrough editor and overseer for the TrueGaming network and has been an avid Xbox achievement hunter for years, accumulating over 700,000 gamerscore to this date. When he’s not writing or gaming, he’s focusing on his physics studies for Queen’s University.
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