Mission: Find the documents in X18Edit
On entering X18 the Find the documents in the underground lab mission leg is concluded (you found the entrance) and as you enter the lab your primary mission changes to Find the documents in X18. As you progress through X18 other related primary submissions are spawned with their relevant sub-tasks.
Since X18 consists of three different floors, finding your way around can be difficult, especially since the minimap shows the layout of all three floors in the same, flat image. I have created a custom map, though, that shows each individual floor - hopefully that may help you find your way; the map also includes a few obstacles that can be found in-game, so it may be easier to pinpoint your exact location using those.
X18 has Poltergeists roaming around, so watch out for crates, paint cans, and other things they may hurl at you; for now there is little you can do about it, except try to watch your back and break anything that can be broken to prevent these items from being used against you.
The starting point is on the top floor of X18. You'll be able to find a dead stalker close by and once you've looted him head down the stairs to the north (taking you down to the middle floor). His body may also be used for stashing purposes.
Mission: Find the codelocked doorEdit
Once you are on the middle floor you should be able to see a door to the south-east (door #1) - approach it and you'll be given a new sub mission (Find the codelocked door) and sub task: Discover the code that opens the door. Both the door and the location of the key-code will be added to your map. Even though you may have played the game before (and therefore already know the code) you won't be able to open the door until you physically locate the code.
Before you go after the code, move into the room to the east, beyond the door; in there you should be able to find two artifacts (Slug and Droplets) along with some anti-rads in the opposite corner of the room from the Fruit Punch anomaly. Once you've taken all the items head out of the room and go north; you should spot a small passageway with two close doorways; there is also a Vortex anomaly located in a hole in the wall. Head to the north-east doorway. There you'll find a room filled with lockers (the middle floor locker room on the map); some of them contain goodies so be sure to go through them all. Notable items include a Monolith Suit and an Akm 74/2 with a GP-25 Kostyer Grenade Launcher attached to it. The Monolith Suit is superior to the Stalker Suit you're likely still wearing, so be sure to pick it up. The Monolith Suit doesn't have night-vision however, you may wish to hold onto your Stalker Suit for a while.
Opposite the locker room, on the other side of the wall with the anomaly in it, you'll be able to find some artifacts; you can find a Wrenched down the small set of stairs and a second artifact (which seems to be random) can sometimes be found in the wooden crate underneath the stairs. (Beware, at the bottom of the stairs is a high radiation area) Move out of the room and back into the room with the locked door. Move through the first doorway to the east and you'll come to a room with a hallway leading towards the north; as you may be able to see, the hallway has some Burner anomalies in it so be careful when you approach (use bolts to accurately pinpoint them). Also, once you get close enough two snorks will appear at the end of the hallway - they will definitely attack you, so again be careful.
On the right side of the hallway you'll spot another room; inside you'll see something resembling a Burner anomaly floating around the room. This is a variant flame anomaly, the Comet. Inside the room you can usually find some Droplets and a dead stalker. Watch the pattern of how the "anomaly" moves around and sprint inside when you've got a clear path. Loot the dead stalker and pick up any nearby artifacts.
Once you reach the end of the hallway you should be really close to the marker on your map; inside a small room to the east you'll find a body of a scientist. Be sure to avoid the burner anomalies. Once you search his body you'll hear a voice message providing you with the code for the door: 1243. Just next to this room you'll find a toilet with an anti-rad in the sink.
Time to backtrack back to the room with the locked door. Once you're there, enter the code and head through the door and down the stairs to the bottom floor.
Mission: Open the door to the control centerEdit
Once down, head inside the room and to the east - approach the door ahead (door #2) and you'll be given another key-code hunt Discover the code that opens the door. Fortunately, the location of the code will again be marked on your map (it's further to the north). The area ahead is filled with Poltergeists (about 6 or 7) so you're likely to be bombarded with various items. Make sure you deal with any Poltergeists you come upon to end their constant battering. During this phase of your mission fitting all of your Spring artifacts and a Slug to your belt will help greatly.
In the south-west part of the floor you'll also come across a room with some lockers in it; two of them have a metal box inside containing some bandages and some ammo. Connected to that is another room that has has a blue stashbox in the far corner, containing more goodies.
Further north you'll come up a small room with some stairs going down; you'll be able to find the keycode down in this area, but take care when you move down - you're about to run into a Pseudogiant; while they aren't really that tough, their stomping attacks can be pretty brutal if you get too close. In the north-eastern part of the room you'll find another body of an Ecologist that will reveal the code to the second door: 9524. If you also brought some NATO ammo, the Ecologist may also be looted for an IL86, although it will be in a used condition, and you may have a lot of other loot to carry out of the level.
Before you leave, check out the small alcove in the south-east part of the room (it has stairs leading up to it); there you can find a blue stashbox and a metal box both containing some goodies, along with a picture of the development team behind.
Mission: Open the door to the control center IIEdit
Backtrack to the door and open it. This concludes the Open the door to the control center sub-mission.
Find the documentsEdit
Before you move on, be aware that there is a special type of enemy ahead - a Pyrogeist - it has a close resemblance to a Poltergeist (except it's red) and rather than using telekinesis to throw things at you it sets fire traps for you.
The documents are through the Control Center door, bear right through the second (open but soon to be closed door), to the right and on a desk up the stairs. As soon as you take the documents that second door will close and leave you with one safe retreat point seen if you turn left at the second door and proceed up a ramp to a nearby supply room.
Furthermore, the external tactical situation within the Dark Valley will alter. Before that you need to immediately assess your situation. You may visit the supply room, loot it and leave the entire facility and transport any loot elsewhere. Provided that you do not take the documents at this point, or attack and kill the Pyrogeist, you are free to come and go. If you have any special loot or a favourite assault / sniper rifle stashed nearby, now is the time to consolidate. About the worst that might happen at this stage is a respawn of the Bandit squad guarding the factory.
Notwithstanding all of this, if you have the documents (and the door is 'locked') then the best strategy for dealing with the Pyrogeist is to make quick sorties from the cover of the supply room ramp to lob an F1 grenade for it to come down the stairs onto. Once you do kill it, you'll pass out and a cut-scene will follow.
Bring the documents to BarkeepEdit
When you wake up again you'll hear a transmission - it seems that soldiers have moved in on the perimeter so expect resistance when you backtrack to the entrance of X18. You'll encounter the first soldier at the top of the stairs leading from the middle floor down to the bottom floor.
Get out of the Dark ValleyEdit
After you pass back through to the factory in the Dark Valley, you will hear two transmissions, the second of which is from Sidorovich telling you to return to Cordon to escape the military presence in your immediate vicinity. You do not need to comply with his ministrations, nor is the exit to Garbage "blocked". Certainly there are Military units within the Dark Valley but none that need worry you particularly.
If you are lucky you may have one or two secret stash markers on your minimap in X18 - one will lead you to a room with a safe in it close to the Pseudogiant's lair. This contains a Monolith Suit and a Night Star artifact - two very nice items in their own right. The other stash is in a backpack in the supply room near the Control Center of X18.