In Doom Eternal’s seventh mission, “Mars Core,” there are 20 exploration items across the entire level, which you’ll be exploring in the three sections: Phobos, UAC, and Meteor. The level’s final section, Hell, has all of its exploration items in plain sight.
While some items, like modbots and codex entries, appear on the map automatically as you explore, a hidden or secret item won’t show up unless you happen to walk nearby. You’ll know you’ve passed by one of these collectibles when you see a white question mark on the map or a large, floating question mark in the game world.
In this guide, we’ll show you where to find all hidden items: two hidden Sentinel Batteries, three hidden Praetor Suit Points, two hidden Secret Encounters, three hidden Toys, one Cheat Code, and two Albums.
Below, you’ll find maps, locations, and explanations of how to reach every question mark and find each secret in this level of Doom Eternal.
Mars Core Sentinel Battery locations
There are three Sentinel Batteries in the “Mars Core” mission. The third one is in the game’s final section, right in plain sight. Here’s how to find the two hidden Sentinel Batteries.
Phobos // Hidden Sentinel Battery
After your fight on the bridge of the BFG-10000, a maintenance hatch will open. Drop down, but instead of following the critical path forward, turn around and jump over the platforms in the opposite direction to find this Sentinel Battery.
Meteor // Hidden Sentinel Battery 02
In the section where you are jumping across multiple platforms to move forward, you’ll eventually make your way to a building at the very end.
Instead of entering the building, turn around and jump back toward the last structure you were at to find this Sentinel Battery on top.
Mars Core Praetor Suit point locations
There are five Praetor Suit Points across the “Mars Core” with some of them off the critical path. Here’s how to find them.
Phobos // Praetor Suit Point 1
In the room inside the BFG-10000 where you find the automap station, you’ll have to move up several pistons to make it forward. On a ledge opposite of the critical path is a Praetor Suit Point.
UAC // Praetor Suit Point 2
After the battle encounter with the buff totem, head down along the critical path into the building. Once inside, instead of moving further into the building, look to your left to see the breakable wall in the gallery above.
Breaking it will reveal a lower area you can drop down into with this Praetor Suit Point and a hidden Secret Encounter.
Meteor // Praetor Suit Point 3
You can find this Praetor Suit Point early on once you use the Ion Catapult to get onto the meteor section.
Follow the images above to find the hallway and shaft upwards past several tentacles to find this suit point awaiting on a high ledge.
Mars Core hidden Secret Encounter locations
There are two Secret Encounters hidden in the “Mars Core” mission.
UAC // Secret Encounter 1
The one can be found right next to Praetor Suit Point 02, detailed above, in the battle arena with the buff totem.
After defeating the enemies there, head down along the critical path into the structure. As you move on, instead of going further into the building, look to your left to see the breakable wall. Destroying it will reveal a lower area you can drop down into where the Secret Encounter is and the Praetor Suit Point.
Meteor // Secret Encounter 2
In the area after the swing bars where you drop down out of the facility and onto the floating platforms outside, instead of moving forward, turn back around to the open door that leads you back into the facility.
From there, find the breakable vent pictured above to reveal a teleporter than brings you right in front of the Secret Encounter.
Mars Core toy locations
There are three Toys hidden in the “Mars Core” mission.
UAC // Toy 1: Prowler
You’ll come across the marker for this hidden toy much earlier in the level, but you won’t be able to access it until right before you complete the mission objective, “Use the Ion Catapult.”
In the area where you find the controls for the Ion Catapult, simply go down the other hallway in that area to find Toy 01: Prowler.
Meteor // Toy 2: Carcass
This one is located right after Secret Encounter 02, listed above.
In the area after the swing bars where you drop down out of the facility and onto the floating platforms outside, don’t go forward, instead turn back around to the open door that leads you back into the facility.
From there, find the breakable vent to reveal a teleporter than brings you right in front of the Secret Encounter. Next to the encounter is a jump pad. Head on up and at the end of the main room behind a zombie is Toy 02: Carcass.
Meteor // Toy 3: Pinky
After the section where you go through several hallways filled with enemies and tentacles, you may notice a locked door with a question mark.
To access it, continue forward once you’ve cleared the enemies by dropping down into the lower level of this facility. Once you’re down there, look to your immediate left to see a breakable vent. On the other side is a jump pad that brings you into that room where Toy 03: Pinky is.
Mars Core Cheat Code location
There is one cheat code in the “Mars Core” mission.
Meteor // Cheat Code - Powerup Mode: Onslaught
Once you’ve fired yourself from the Ion Catapult toward Mars, you’ll enter a facility with a handful of connected corridors.
Right after the first small encounter, follow the map above to find the Cheat Code - Powerup Mode: Onslaught sitting at the end of a hallway.
Mars Core Album locations
There are two albums in the “Mars Core” mission.
Meteor // Album: Doom 64 - Intro
In the area right where you find Praetor Suit Point 3, along the critical path once you use the Ion Catapult, you’ll see a jump pad and several swing bars.
Instead of moving forward after hitting the first jump pad, turn around and you’ll see a question mark on a small ledge. Use the swing bars and jump over to it to get the Album: Doom 64 - Intro.
Meteor // Album: Quake Champions - Goroth
In the area filled with several tentacles and enemies, you’ll find a control panel in the center of the facility. Hitting its button will move a glass wall next to it, revealing a platform and two breakable vents flanking the platform.
Jump on top of the platform and break the vent to the left to find the Album: Quake Champions - Goroth.
Mars Core Slayer Key location
A Slayer Key is hidden in the “Mars Core.” You need the Slayer Key to open the Slayer Gate, which gets you one of the six Empyrean Keys.
Meteor // Slayer Key
The process of getting this Slayer Key is the same as getting the Album: Quake Champions - Goroth.
In the halls filled with tentacles and enemies, look for the control panel in the center of the area. Activating it will push a wall back around the corner, revealing a platform and two breakable vents. The one to the right will lead you to the Slayer Key.