Mission: Free the DutyerEdit
When you enter Dark Valley you'll notice a couple of dots on your minimap - they indicate Bullet, a Duty member, and a wounded bandit. Move up to Bullet and he'll ask you to help him free a fellow Duty member. This mission, Free the Dutyer, will net you a PSO-1 Scope so be sure to accept, and follow Bullet as he moves east to an ambush point. When get close to the road the mission will be updated and you are prompted to Kill the bandits and rescue the Dutyer. Do as Bullet tells you and hide behind the building on the western side of the road. Soon you should able to see the mission marker on your minimap move closer, approaching from the north; this is the Duty member who's being escorted by two bandits. Once you've killed the bandits and talk to Bullet he'll give you 1300 RU and a PSO-1 Scope.
Vasko Magnate, the guy you just rescued, will be able to give you another optional mission; apparently another Duty member is being held prisoner at the bandit HQ, the place you're headed, so you may pick up this mission if you wish; it doesn't come with a reward when you complete it, though, but may improve your status with the Duty faction
Mission: Find the documents in the underground labEdit
Once you're ready to move on take a look at your map; to the north of your current position is the Bandit Base - and to the west of that, you should be able to see a green marker with the description "pipe" - this is a secret entrance to the HQ, so head in that direction.
Once you reach the pipe, climb inside and move forward. Your mission will be updated and you'll now need to find Borov and take the key from him. Right after you come out of the pipe on the other side, turn left and move into the pipe there. Along the way in this trench you'll notice a bandit on your right side - don't attack him since you'll be in a vulnerable position. Once you reach the end of the trench you'll come up by the northern building at the bandit HQ.
You may see a yellow dot on your minimap, indicating a neutral person - although this is a Duty member, it's not the one you have to break out of prison so don't worry if he should die in the ensuing firefight. A second yellow dot may be seen on the minimap, along with several grey dots, the PDAs of dead men. Inside a building a short distance off from the Bandit Base, the culprit can be found along with the bodies - a Bloodsucker. This is a close quarters environment, so be wary.
Once you've dealt with any bandits in the vicinity, move inside the main hangar and up the start on the right side. Follow the walkway and you will eventually move inside the building next to the hangar. The building can seem like a maze since it has several floors with stairs going up and down every now and then, but what you simply need to do is head south. You'll find Borov's office on the 1st floor. Borov should be fairly easy to locate since he will be marked on your map.
On your way to Borov's office you should run into an experienced bandit Friar (dressed in a trench coat) - he's carrying the weapon required for the Find the weapon of the Dutyer mission so be sure to pick up the unique weapon when you've dealt with him. You can of course also search for him after you've dealt with Borov, but I personally tend to run into him on the way there.
You're very likely to find Borov in his office, on the 1st floor (i.e., one floor above the ground floor) of the building. Once you reach him, kill him, and search his body and you'll obtain the second key to X18, and your mission will be updated now prompting you to get out of the bandit base. Before you do, you may wish to head downstairs and locate the storage room and the cellar nearby, containing the imprisoned Duty member. Inside Borov's office you'll be able to find a lot of goodies including bandages, medkits, food, two VOG-25 grenades, and some 5.56x45 mm AP rounds.
In the cellar, where the Duty member is held prisoner, you can also find a Merc Suit but since you probably already have upgraded to the Stalker suit, you might as well leave it and save your carrying capacity for more useful items.
The strong room should be easy to spot when you search around the HQ. Inside the room you'll be able to find a lot of goodies including bandages, antirads, ammunition, a ton of Vodka bottles, and more. Nothing really important or noteworthy, though.
Before you leave you may wish to seek out the various hidden stashes that you've likely uncovered by killing and searching the bandits in the HQ. When you're ready to leave the HQ you can either head towards the gate (which is northeast in the HQ) or towards the marker on your map - that will lead you out through an elevated tunnel. You may have have discovered a secret stash inside the elevated tunnel, so that is usually my preferred way of getting out of the HQ.
As you leave the HQ your mission will be updated and you now have to locate the entrance to the X18 lab. Since you're probably loaded with equipment and artifacts, you may wish to head back to the Bar to off load or sell your loot, but also to finish the optional mission, Find the weapon of the Dutyer, given by Brome. When you return to him he'll give you a Slug artifact as a reward. If you hate to give up the Storming Obokan there is a nice trick available showing you how to get it back.
Before you head off to X18 there are a few things that are good to know. First off, inside X18 you'll find the Monolith Suit that is superior to the Stalker suit, so even if your current armour is worn out there is no need to replace it - you'll find a better armor in X18. Also, you will find the GP-25 Kostyer Grenade Launcher which can be attached to an Akm 74/2 - so if you're still using one, you may wish to bring along some VOG-25 grenades if you have any.
Another helpful secret is in the building that contains the actual entrance to X18, there is a flight of stairs that leads to the higher floors and the roof of the building. If you start to climb these stairs and look to your right, you will see an area in the corner with pipes coming out of the wall. If you jump onto these pipes, you can climb to the top of this corner area where you will find a steel box. Hack it open with your knife or push it back towards the main room to break it and 300 9x39mm SP-5 rounds will be yours for the taking.
Mission: Find the entrance to the labEdit
The entrance to the X18 lab can be found in the cellar inside the main building of the factory in the western part of Dark Valley. There are plenty of bandits around so be careful once you're inside the gate. You can find an RPG-7, though due to its sheer weight and extreme rarity of ammunition dragging this weapon along may be more of a burden than an actual help.