The DOOM series is mostly famous for its awesome combat, but there’s a decent amount of lore tucked away too. In DOOM: The Dark Ages, you’ll see this in the story, world details, and 26 collectible codex entries spread across its 22 chapters. These entries give extra info on characters and places, and grabbing them all unlocks the Lore Nerd Trophy/Achievement while boosting chapter completion. Here’s a rundown on where to find each one, with maps for exact spots.

Codex 1: Doom Slayer (Chapter 1)

Doom The Dark Ages Codex1 Doom Slayer

 

When you’re taking out the four Demonic Portals, look behind one for a path with a climbable wall. Head up to grab the Doom Slayer codex.

Codex 2: Village of Khalim (Chapter 1)

Doom The Dark Ages Codex1a Village Of Khalim

Near the end, after clearing demons to drop a red forcefield, follow the path until you see a climbable wall on your right. Climb it to find the Village of Khalim codex near some Sentinel soldiers.

Codex 3: Hebeth (Chapter 2)

Doom The Dark Ages Codex2 Hebeth

Early in Chapter 2, after pulling a lever to open a door, drop into the next area and go straight through a doorway with green light strips. Turn left, jump over some crates, and you’ll find a secret spot with the Hebeth codex.

Codex 4: Sentinel Barracks (Chapter 4)

Doom The Dark Ages Codex3 Sentinel Barracks

At the end of Chapter 4, when heading to the Dragon’s Den, you’ll hit an open area with a Sentinel Shrine. Before going in, take the left path to score some gold and the Sentinel Barracks codex.

Codex 5: Deag Loric (Chapter 5)

Doom The Dark Ages Codex4 Deag Loric

Halfway through Chapter 5, while destroying four Hell Carriers, you’ll reach the core of the one under the cathedral (where the Cycler is). Backtrack under the metal railing you dropped from to pick up some gold and the Deag Loric codex.

Codex 6: The Holy City of Aratum (Chapter 5)

Doom The Dark Ages Codex 5 The Holy City Of Aratum

After grabbing the Super Shotgun, head into the nearby building and take the first door on your right. You’ll end up outside by a metal cross—smash it with your shield, then shield charge the block to climb the ledge near the Super Shotgun container. Follow the wooden scaffolding, re-enter through a broken window, and find the Holy City of Aratum codex down a long hallway.

Codex 7: Siege - Part 1 (Chapter 6)

Doom The Dark Ages Codex6 Siege Part 1

In the Gore Portals section of Chapter 6, you’ll pass an area with an Atlan fighting a Titan in the background. Check for piles of debris you can jump on—one has the Siege - Part 1 codex.

Codex 8: Kreed Maykr (Chapter 6)

Doom The Dark Ages Codex7 Kreed Maykr

On a far side of the map, near shallow water with enemies, find a Sentinel Shrine. From there, head to the map’s edge to spot a climbable wall. Climb up for the Kreed Maykr codex and some gold, close to the Mancubus collectible toy.

Codex 9: Siege - Part 2 (Chapter 7)

Doom The Dark Ages Codex8 Siege Part2

If you picked up the Chapter 7 secret key, use it to unlock a gate. This leads to a path with gold and two shield enemies. Take them out, and the Siege - Part 2 codex is yours.

Codex 10: Abyssal Forest (Chapter 8)

Doom The Dark Ages Codex9 Abyssal Forest

While moving through the barracks in Chapter 8, hug the right wall until you reach a row of shield enemies. To the right, break through vines with a shield charge to find the Abyssal Forest codex.

Codex 11: Ancestral Forge (Chapter 9)

Doom The Dark Ages Codex10 Ancestral Forge

Near the spectral wolf statues in Chapter 9, drop off a ledge onto a wooden platform. The Ancestral Forge codex is there with some gold.

Codex 12: King Novik (Chapter 9)

Doom The Dark Ages Codex11 King Novik

In the underground area with moving platforms, you’ll throw the Shield Saw at a blue gear to keep going. Backtrack to the previous platform, face the gear, and look up for a red metal cross you can break with a shield throw. Use the blue gear to raise the platform, but instead of moving on, jump back to the lowered platform. Use the green shield statue and some jumps to reach the King Novik codex.

Codex 13: The Forsaken Plains (Chapter 10)

Doom The Dark Ages Codex12 The Forsaken Plains

During the “Destroy the Hell Cannons” section, find a Sentinel Shrine near a spiked metal plate that drops when you approach. Head away from the shrine toward the plate, and you’ll see gold trails—one leads to the Forsaken Plains codex.

Codex 14: Prince Ahzrak (Chapter 10)

Doom The Dark Ages Codex13 Prince Ahzrak

If you grabbed the Chapter 10 secret key, use it to open a gate near the fallen Atlan. Inside, you’ll find demons, gold, and the Prince Ahzrak codex.

Codex 15: Sentinel Command Station (Chapter 12)

Doom The Dark Ages Codex14 Sentinel Command Statio

Early in Chapter 12, after exiting some vents, stick to the right wall. You’ll find gold and the Sentinel Command Station codex.

Codex 16: Spire of Nerathul (Chapter 14)

Doom The Dark Ages Codex15 Spire Of Nerathul

Early on, when draining water to reach a Stasis Emitter, check a ledge where the water was flowing for the Spire of Nerathul codex.

Codex 17: Serrat (Chapter 14)

Doom The Dark Ages Codex16 Serrat

In the “Release the Old One” section, climb a derelict structure to an elevator triggered by a green platform (a point of no return). Before stepping on it, check a path to the right of the elevator entrance for the Serrat codex.

Codex 18: City of Ry’uul (Chapter 15)

Doom The Dark Ages Codex17 City Of Ryuul

During the “Activate the Portal” section, look for a ledge on one side of the map. Drop down to find a gold trail and a climbable wall—up top is the City of Ry’uul codex.

Codex 19: The Witch (Chapter 16)

Doom The Dark Ages Codex18 The Witch

Find a metal grate near the map’s center. Follow the rocky outcrop, jump to a platform with armor pickups, and spot a blue gear through a hole in the chamber wall. Throw your shield at it to raise the grate and grab The Witch codex.

Codex 20: Temple of Lomarith (Chapter 17)

Doom The Dark Ages Codex19 Temple Of Lomarith

In the first big underwater section, look for an upturned shipwreck floating nearby. The Temple of Lomarith codex is inside.

Codex 21: Commander Thira (Chapter 18)

Doom The Dark Ages Codex20 Commander Thira

 

In the “Destroy the Organ” section, find the Commander Thira codex in a gap in an inner wall. Get there by following the path to the upper area of the beast’s belly and running through stomach acid.

Codex 22: Harbor of Souls (Chapter 19)

Doom The Dark Ages Codex21 Harbor Of Souls

This one’s out in the open to the left of the main path, super easy to spot if you’re checking the map for collectibles. That’s the Harbor of Souls codex.

Codex 23: Hell Priests (Chapter 19)

Doom The Dark Ages Codex22 Hell Priests

At the final point of no return, after the flames and moving metal platforms, turn around and take the left path. It loops to the Hell Priests codex.

Codex 24: Resurrection (Chapter 20)

Doom The Dark Ages Codex23 Resurrection

Drop from the ledge behind the yellow key to find a key door on your right. Behind it is the Resurrection codex and the Cosmic Baron collectible toy.

Codex 25: Commander Valen (Chapter 20)

Doom The Dark Ages Codex24 Commander Valen

After destroying the siege towers and flying up on the Slayer’s dragon to the Kreed ship, turn around right after landing. The Commander Valen codex is on the edge of the landing pad.

Codex 26: Marok (Chapter 22)

Doom The Dark Ages Codex25 Marok

After shield charging through the green gate at the start, you’ll overlook a big battlefield. Don’t jump into the fight—take the right path to find the Marok codex. If you’ve collected all the others, this one unlocks the Lore Nerd Trophy/Achievement.