Chernobyl Interior
Many Monolith soldiers patrol the interior, with most of them wearing military exoskeletons. Although the first one you encounter drops a gauss rifle (likely the first one you’ll actually be able to pick up), it, and any other sniper rifles you have, won’t be of much use in the cramped quarters here. Best to stick with your GP 37, if you’re still using it, or another assault rifle, and go for headshots. Even the nice shotguns these guys drop won’t be of much help against their exoskeletons.
Now, if you wish, you can find an exoskeleton here of your own. If you follow the corridors in front of you, you’ll eventually note that it splits off into two directions. Through a door to your left, there’ll be a concentration of four or five soldiers, while around the corner to your right, there will be a couple soldiers with shotguns and a room full of vertical piping. In the corner of the piping room is a ladder leading downward. There’s a stash here with a bunch of ammo and an exoskeleton suit for you, but the exoskeleton suit weighs a full 15 kilograms, and only gives you a 30% radiation protection rating, meaning that you’ll get slowly roasted if you attempt to wear it, at least without a number of anti-rad artifacts on your belt.
After wading through the soldiers through the doorway, in the room that acts as their barracks, look around on the floor; one of them will likely have dropped an FT 200M rifle. It won’t have quite the same amount of accuracy as your GP 37, but will deal a bit more damage. The extra recoil might make it not worth your while; it’s up to you.
The Wish Granter
Anyway, adventure on until you reach a stairwell leading up to a set of square hallways that all connect to one another. There are two paths to take here. One, near the southeast corner of the hallways, will lead you up to the Wish Granter and one way to end of the game. Climb over the rubble and find the ladder leading upwards. When you enter the Wish Granter room, find the small, pulsating white teleporter and jump to it. It'll warp you to the top of the room. Follow the path in front of you around the room until you reach the Wish Granter, then touch it. It'll apparently give you different endings based on certain character attributes. We had over 200,000 RU on our character, so we got a rather negative ending based around our character's desire to be rich.
The Secret Lab
In the northern hallway, though, in the set of square hallways below the Wish Granter chamber, there’s a ladder in a doorway underneath a rotating yellow klaxon light. If you head up there, you’ll be able to use the electronic decoder you obtained in Pripyat. Head to the door up there, use it, then wait 30 seconds until it opens to head through. Soldiers will assault you while you’re waiting, spawned somehow by the Monolith, so hide behind the metal boxes near the door and keep them back with grenades until you can safely make it through to the Secret Lab. If you manage to duck behind the larger boxes, though, you can simply crouch down until the door opens; none of them will notice you and thus you won’t have to fight any of them.
The lab here is, again, full of enemies, and there are some annoyingly long hallways to fight through. After entering the level, you’re going to want to head down the hallway to your left first, so concentrate on taking out some of the soldiers there, then dashing forward to the small alcove across the hallway there, which you can use as cover. There are going to be gauss-rifle using soldiers firing on you from the far end of the hallway, so try to avoid exposing yourself as best you can.
When you enter the hallway to your left, you’ll have to start fighting your way to the corner of each hallway, taking right turns at each of them. Stick to the small off-rooms, but be aware that there are going to be soldiers in some of them, so quicksave often!
Eventually you will reach a control room off to the left of the set of hallways that you're exploring. Grenade out the soldiers inside and enter the small, darkened room here. If you want to visit any parts of the game before the end, then make a full save here, as the door will close behind you after you head through.
The True Endings
When you enter the final room here, the door shuts and you're stuck in a room with six or seven small purple contraptions sticking up out of the ground. Gosh, they look important! You should probably shoot them, then!
As you blast away at the pillars, flame anomalies will open up around you. Ignore them as best you can as you fire away at the pillars. When all of them are destroyed, you'll begin speaking with a Matrix-y fellow who will tell you a bit of the backstory behind your adventure thus far, then offer you two choices. If you agree to join the consciousness project, then the game will end with a cinematic cutscene. If you refuse, however...
Returning Control To Humanity
The consciousness group will teleport you outside of Chernobyl, into the "backyard" of the facility, so to speak. You'll be able to return to the interior zone, if you wish, but all you will find is a locked door.
Anyway, the field outside of where you're teleported is full of junk, and will soon be full of soldiers that will be teleported in to fight you. Protect yourself as best you can from their gunfire, shooting them if necessary, until you can reach another one of the little while teleportation devices here.
At this point, your adventure is only just beginning. Each of the little white teleporters will send you to another zone of the field that you're in. Your goal is to reach a teleporter, warp to another small area, clear it of enemies so that you can explore, find another teleporter, then repeat the process. Some of the teleporters are hidden from sight; for instance, one of them will require you to jump through a broken barricade atop a building and fall through the warp. Finding the warps can be difficult, as can surviving the enemy assaults.
After a long series of warps, though (perhaps 20 or more total), you will eventually warp right into a cutscene that apparently represents the "best" ending to the game.