UAC Atlantica Facility

UAC Atlantica Facility is the first level of The Ancient Gods, Part One, the first expansion for Doom Eternal. The level is set on the UAC Atlantica, the UAC's oceanic climate and environmental research station, which secretly conceals the body of the Seraphim - the Doom Slayer is tasked with finding this being in order to free Urdak from the demons' control.

Lore
The Atlantica ocean platform was known as the UAC's primary climate and environmental research station. Hundreds of scientists and engineers produced critical work there during the earliest days of the worldwide energy crisis before Argent energy was introduced.

The existence of a second facility below, cloaked in the depths of a deep trench, was kept hidden to everyone, including the workers on the facility above. The concealed lower structure houses the original body of the Seraphim, stored there after he transferred his consciousness into a cloned human body in order to move freely within the populace.

Objectives

 * Get the Seraphim's Key
 * Locate the Seraphim

Keycards
Turn left and follow the walkway past some zombie cultists; a red slipgate will open in front of you and deposit a mancubus, followed by two Hell knights and two revenants. Head downstairs to the floor below and follow the walkway round to a green-lit door; a dread knight will burst through it as you approach, with a carcass and mancubus close behind. Head through the open doorway to find the blue keycard, then return to the previous room to dispose of a Hell knight and carcass that appear along with some blaster soldiers. Once the door leading outside is unblocked, go through it but be ready to deal with even more demons including arachnotrons, cyber-mancubi and cacodemons followed by a baron of Hell. Once everything is dead, head back up the stairs and go through either of the doors marked "Blue Access".

Whichever door you have used, continue on through an open doorway to a larger hall with a control panel; before you can use it you must dispose of a dread knight followed by some cyber-mancubi. Use the hand scanner on the control panel to unlock the door on your left, go through it and jump to the monkey bar in front of you to swing over to a platform with an arachnotron (sniping its turret with the precision bolt will stop it attacking you on the way over). Dispose of the arachnotron and another mancubus that arrives from the left, then go through the green-lit door to find a turret waiting for you - the eye is the only vulnerable spot, but precision bolts can quickly destroy it. Head past the turret to an arena that has some more turrets scattered around; your attempts to kill them will be hindered by the various heavy demons that teleport in, but there is an Onslaught powerup above the arena you can reach with a monkey bar. Once the arena is clear you need to climb up to a high platform on the side of the arena facing the water then use a monkey bar to reach a cracked grate; punch through it to enter a vent then follow this to the room containing the red keycard.

Seraphim's Key
Leave the room through the door marked "Red Access" to discover that more demons have appeared outside, starting with revenants and Hell knights followed by cacodemons and barons; additionally, parts of the floor are electrified so avoid standing on those areas. Clear the arena again then go back to where you faced the first turret - lasers will activate ahead and some lost souls will appear along with a dread knight, so kill them then head through the next door to face a marauder guarding an elevator. Kill the marauder then step into the elevator and press the switch inside it to head to the upper levels; once you step off and get rid of some zombies, look left to see an arachnotron and two turrets on the other side of a gap with a blowing fan; shoot the green switch on the fan to disable it before you make the leap across or you will get blown away. Once across the gap, dispose of another turret above along with a cyber-mancubus and two cacodemons then head up the steps to find a punch switch that will lower a crate suspended from a crane. Once the crate is close enough, swing to it from a monkey bar and it will carry you up to the tower above.

To reach the tower, you must swing across two monkey bars to get to a climbable wall, while also shooting the green switch above you in mid-air to disable another fan. Climb up the wall to enter a circular chamber with some blaster soldiers and arachnotrons, but use caution as much of the floor is electrified. Head in the direction of the large central facility but use caution as two carcasses will jump on to the walkway followed by an arch-vile. Once the arch-vile is slain, turn towards the tower to see a fan behind you, shoot the green switch to activate it then dash towards the monkey bar over the water; the fan should propel you to a climbable wall far ahead. Jump left off the wall to a walkway with some revenants, then go up two sets of stairs and turn round to see a monkey bar leading to a climbable wall; go to the top of this wall then turn round and jump back towards the monkey bar you just used, which should give you enough momentum to reach a green-lit platform above it.

Follow the walkway here past three turrets and a dread knight to a wider area, where you will have to contend with a cyber-mancubus, carcasses and two barons followed by cacodemons, a pain elemental and a Doom hunter. Once they are all dead, go up the stairs and pass through the green-lit door to enter the facility. Go up another staircase and time your run past a laser grid, then turn left to approach the door in front of you - it will lock and you will have to deal with a marauder that appears behind you. After killing the marauder, use the hand scanner next to the door to unlock it again and acquire the Seraphim's Key.

Destroyed facility
After the cutscene, go through the door in front of you and head straight on to a monkey bar that you can use to reach a large arena ahead; you will have to contend with a variety of enemies starting with arachnotrons and finishing with a tyrant, so make sure to use the Onslaught powerup on the bottom floor if things get tough. Once the arena is clear, go through the door at the back of the arena and proceed down a hallway with tentacle holes until you see a mancubus emerge from a doorway to your left, then go through it and pass through the door ahead to a walkway where you will find another mancubus joined by a cyber-mancubus, two revenants and two Hell knights. Head up to the top floor and go through a door at the top to enter a passage with a fireball launcher, then follow the passage to another door leading outside where some blaster soldiers are guarding a punch switch. Strike the switch then look left to see a crate suspended from a crane heading your way; once the crate is close enough, use the monkey bar to swing to it and let the crate carry you to a climbable wall.

Go up to the top of the wall and look right to leap to a platform above you, then turn left and head through the door in front of you to enter another arena, starting with cyber-mancubi and ending with a baron; mid-way through the battle a buff totem will spawn behind the boxes on the top floor, so destroy it before engaging the heavy demons again. After clearing the area, head through a door on the bottom floor to a room with an electrified floor and kill the revenants and imps that appear there then jump across the crates to deal with a turret and a cyber-mancubus. Head up the stairs and follow the path to find a dive suit, then go through the door next to it and follow the passage to a submersible device that you can use to reach the Seraphim's location. After the cutscene, swim forward towards the indicated building (watching out for an oxygen tank guarded by a shark) then go under the building to find a point where you can surface. Go through the door in front of you and kill the mancubus blocking your path, then go through the door on your left and follow the tunnel until you get to some shield soldiers in front of a turret; they will be joined by two dread knights and then a tyrant and some carcasses, so kill everything then head through the door behind the turret to a room where you have to dive into the water again.

Follow the trail of submerged items in front of you until you can surface again and do so, then go through the center door - the tunnel will explode and water will flood in, so swim forward to the central shaft and get on top of the inactive elevator in front of you to surface. Use the climbable walls in the shaft to get up to a circular ledge where revenants and turrets are shooting at you, then press the green hand scanner to call the elevator and ride it up to the final arena. There is an apparently unlocked door on the bottom floor, but when you approach it the door will lock and two marauders will emerge from slipgates behind you; once they are both killed the bottom floor will be electrified and waves of heavy demons will start teleporting in, starting with mancubi and building up to two tyrants along with multitudes of imps. Once all the opposition is finally destroyed, go through the door you tried to use earlier and use the hand scanner behind it to finish the level.

Slayer Gate
When you enter the corridor with tentacle holes, head all the way along it to a room with two laser grids - which have the Slayer Gate between them - then continue on to find the automap station, though you will have to dispose of a tyrant to reach it. Climb on top of the crate next to the automap station, then stand on the fence and look down to see one or two monkey bars. Swing off both monkey bars (ignoring a turret on the left) and turn right in mid-air to dash to a cracked grate, then follow the vent behind it to the Slayer Key.

In addition to all the fodder demons, the heavy demons in this encounter tend to be paired - cyber-mancubi and revenants, arachnotrons and dread knights, whiplashes and Hell knights, carcasses and an arch-vile, and finally a tyrant and a Doom hunter. Completing this encounter will reward you with a support rune to be used alongside the standard runes.

Secret encounters

 * 1) After riding the first elevator up, drop off the edge of the platform you are standing on to find a second platform just below with a gore nest. You will have 25 seconds to kill a mancubus, two carcasses and two zombies.
 * 2) Shortly after the corridor with tentacle holes you will fight some enemies on a tiered walkway; at the top of this walkway is a control room containing a dive suit which you will need for the next part. Interact with the green hand scanner near the dive suit, then head back down the walkway and jump into the deep water here - three submerged chambers have opened, and the left-hand chamber has a cracked grate with a launcher behind it that will propel you up to the gore nest. You will have 15 seconds to kill six spectres and a zombie.

Completing both secret encounters will unlock the "Industrial Espionage" Slayer skin.

Special items

 * Four extra lives
 * In the vent leading to the red keycard, instead of heading towards the key go away from it until you see a hole in the ceiling. A 1UP can be found in this hole.
 * After riding the second crate suspended from a crane, jump to a climbable wall and use it to reach an overhead platform. Turn right at this point and follow the platform to a 1UP; dread knights will climb up as you approach the pickup, and an arch-vile will spawn behind you after you collect it.
 * At the underwater structure, when you enter the water for the second time you must follow a trail of items to a point where you can surface. Ignore that point for now and continue following the curved tunnels round until you get to another point where you can surface; go through the only door in this room that opens and follow the tunnel round to a 2UP.
 * Four soulspheres
 * After passing through the Blue Access doors and using the control panel to open another nearby door, go outside and head down the stairs to find a soulsphere.
 * A soulsphere is hidden in the fenced area of the electrified circular chamber, which you can reach by jumping off the nearby crates.
 * Dive into the deep water pool containing the second secret encounter and look in the far corner for a cracked grate. Dash through it then follow the vent up to a second grate with a soulsphere behind it.
 * After swimming to the shaft in the middle of the underwater structure, look under the oxygen tank to see a crack in the floor with a soulsphere underneath it.
 * Two Argent cells
 * Collect the first dive suit and use the green hand scanner next to it, then drop into the deep water pool below and enter the middle chamber to find the Argent cell.
 * At the top of the final arena.

After finding the red keycard, backtrack to the room behind the Blue Access doors. There is a door here marked "Red Access"; open it to find a secret ammo cache.

After finding the first dive suit, destroy the cracked grate above and behind it to find a secret armor pickup.

Collectibles

 * Four Codex pages
 * "Book of the Seraphs - Part I" - taking the first soulsphere will unlock the door next to it, letting you return to the blue keycard room. Go through the next doorway and turn right to see that another door has opened; the page is behind it.
 * "Book of the Seraphs - Part II" - up the steps by the first punch switch.
 * "Book of the Seraphs - Part III" - after reaching the walkway before the central facility, head to a sealed door and look for a curved ledge next to it. The page is at the end of this ledge.
 * "Book of the Seraphs - Part IV" - after entering the central facility, look behind the staircase for this page.
 * One support rune
 * A support rune is given for completing the Slayer Gate encounter.