[Necromancer]

The Dark Valley

Reaching the Dark Valley will require you to head through some irradiated segments of the Garbage. Your stalker suit will help you resist most of the rads, but you still might want to slip on an artifact that helps you resist the rads if need be.
The Dark Valley has plenty of artifacts lying around, as well as some special non-mission encounters. To the east, above the location marked Lab Entrance, you can find a rocket launcher with one round of ammo on the third floor of a large building. To the south, in the middle of a farm, a stalker will sell you a gauss rifle for 800 dollars, then scam you and refuse to hand over the merchandise. Feel free to kill the stalkers there if you like, but there’s no gauss rifle to be found.
When you reach the Dark Valley, a simple side mission will be offered to you. You can skip it if you like, but it will tie in with your main goal here, so we’ll go ahead and describe it.

Follow Bullet To Ambush Location

The first time you enter the Dark Valley, you’ll come across a Duty soldier who’s incapacitated a bandit. Apparently the gang of bandits have captured one of the Duty soldiers and will be holding him for ransom, but if you ambush them before they can reach safety, you can free the soldier and hopefully get rewarded.
When you reach the ambush point, wait across the road from Bullet, behind the small structure there. His soldier friend will be the first to enter your line of sight; two bandits will follow. Wait for Bullet to open fire, then take out the bandits. Speak to Bullet for your reward. He'll reward you with a PSO-1 Scope that can probably be attached to your rifle, assuming you're carrying the right kind.
After you complete the mission, speak to Borya for some more information regarding the factory where Borov is holed up. If you speak to him thoroughly, he’ll give you the "Free the Dutyer from the Bandit prison" mission.

Find The Documents / Free The Dutyer

Both of these missions can be performed at the same time. Before you head in, you might want to poke around the map a bit. You probably have plenty of stash markers around here, and there’s some decent stuff to be found. One item of particular note that’s not in a stash is an RPG-7u rocket launcher with one round of ammunition. It can be found on the top floor of the structure in the eastern side of the zone, surrounded by bandits.

Sneak Into The Base

The bandit base to your north is where you need to go to find the second key to the lab. There’s a pipe on the western side of it that will lead underneath the wall. Find it and head inside, then take a left to reach dry ground.

Take the Key From Borov

Borov is a bandit, and isn’t going to just hand the key over to you. You’re going to have to fight your way through plenty of soldiers in order to find him; he’s holed up in one of the buildings on the southern side of the little complex. He can be tough to locate since he’s on the second floor of the building, and his marker on your map might actually indicate that he’s outside, but he should be inside the building. It’s laid out like a level from a normal FPS, so you won’t be able to head directly towards him; you’ll have to enter from the north and fight your way through plenty of soldiers in order to reach him. When you reach the stairwell in the middle of the brick building, you can poke around a bit for the stairs leading down to find the Dutyer soldier, who’s being held in a prison in the basement. You need to flip the switch on the wall nearby with your use button to let him out. If you do so, though, he’ll pick up a gun and might help you out in the fights.
Anyway, Borov is located deep within the building here. He can be complicated to find, but you’ll probably wind up just running up some steps and getting blasted by soldiers; that’s when you’ll know he’s nearby. Find him, kill him, grab the key off of his body.

Exit the Base/Enter the Lab

You don’t need to exit the base via the marker pointed out on your map; anyway you can get out will work fine. Head to the south to reach the lab entrance; it’s in another set of buildings. Enter via the main entrance, head into the building on your left, then kill the soldiers around the bunks. The entrance is at the bottom of a set of steps inside the locked foyer-esque room to the right of the bunks.