Chapter 4. Office Complex [Black Mesa]
1st Floor
Climb into the breach in the wall on the right next to the electrified wet floor. You can go left along the ventilation shaft and grab 3 clips and a battery there. Crawl along the ventilation to the right. You'll find yourself in an office with a scientist. Press the lever here to turn off the light. Now you can walk across the wet floor without getting hurt.
Exit through the door, then you'll have to climb through the window. The main path is on the right, past the electrified window, but first, go left. There are several zombies on the way. Go into the basement and see a guard behind the bars. Quickly draw your pistol and kill the zombie that approaches the guard from behind. If the guard survives, you'll be able to get into his vault and grab a first aid kit and a shotgun. On the way back, 3 electric aliens will appear. There's a first aid kit and a battery below. Take the guard (1) with you and lead him to the window above.
We break the glass and climb through the window. There's electrified water on the floor in this room, so you can only move around on the furniture, not on the floor. We reach the entrance to the ventilation shaft on the far wall, entering a locked corridor. We open the doors on this side. We go through the room on the left to unlock the door for the guard.
In the corridor with the stepladder, we climb up into the ventilation duct. We emerge into a room with a firing cannon. We quickly run under it and pull the lever behind the grate. There's a stationary first aid kit next to the cannon at the top. We continue on and climb the stairs between floors.
2nd floor
There's a guard (2) on the landing. Go into the offices together. Climb through the window and open two double red doors. You'll have to fight some Vortigaunts here.
Go into the far right corridor and you'll see a door blocked by a white cabinet. Break through it. Inside is a stationary first aid kit and a scientist (3).
If you don't want to complete the achievement, go through the opposite red double doors and exit to the landing. Enter the room with the scientist and use the stationary first aid kit. Leave the guards downstairs, destroy the automatic cannon upstairs, and only then lead the guards away.
3rd floor: Freezer
Follow the corridors. There are two Vortigaunts on your way; blow them up with the nearby explosive crate. On the left is a descent into a dead-end garage; there are three ammo clips and a first aid kit there. On the right, upstairs, is a stationary first aid kit and a guard (4). There's a hidden entrance to the ventilation duct in the wall to the right of the first aid kit. Turn off the fan inside. Upstairs on the left you can find two clips and two batteries. To the right is a locked room and two more clips.
Follow the guards to the center of the floor, where you'll find a cafeteria and a crowd of zombies. Leave your companions here and climb through the red double doors. Along the way, use two vending machines and a stationary first aid kit.
Enter the freezer with food supplies and meet a scientist. Climb the inclined shelves on the right into the ventilation duct. Find the first grenades behind the nearest grate. The next freezer is behind the far grate.
Kill the zombies and the crocodile monster. In the right corner, near the red light, take the valve and insert it into the socket on the left. Rotate it until the platform under the ceiling lines up with the ventilation openings above. On the right, climb the boxes into the ventilation shaft, return to the first freezer, and crawl along the initial ventilation shaft to the catwalk.
In the dead-end ventilation shaft on the right, grab the battery and crawl further left. In the small room, climb up and enter another ventilation shaft. Eventually, you'll emerge onto a landing where a guard (5) and a scientist (6) are standing. There's also a shotgun here. Proceed into the red corridor, bring the remaining guards here, and leave them downstairs.
4th Floor
Go up one floor. You can see a G-Man through the glass in the door on the right. There are several zombies and Vortigaunts in the corridor. Once we've killed everyone, bring the guards and scientists to the elevator; they'll remain here to await evacuation.
In the elevator shaft, jump to the stairs on the opposite wall. Climb higher, jumping over the stairs and plank floors. Finally, jump onto the elevator, go down, and press the button. Next chapter " We have enemies! "
Source: gamesisart.ru.