Map 1[edit]
The hole you need to enter is a mid-way up. While being under the floor turn right two times and enter the corridor. The first guard is standing in a room with his back to you. Easy prey but once you enter the corridor, three guards will spot you.
Follow the corridor, turn left and you will see a scientist behind open door on the right. Kill him if you need more health or just for fun. At the next corner turn right and up the ladder. You can't climb the ladder like humans and predators, so use wallwalk.
Enter the only accessible corridor and follow it to the dead end. You need to climb the wall on the left, but first destroy the grille near the ceiling. Use the night vision if you don't see where to go, the path is hidden in the shadows.
Once above the corridor, go to the vent straight ahead until you come to another path above corridors. Turn left and smash the grille. A number of guards will hurry to see what's all the fuss is about. You can get rid of them without being spotted. Bite the head of the nearest guard without going down. Take your time to aim, he won't spot you. Another guard will take his place. Bite his head off and so on until there are no humans left. This solution doesn't always work but you can kill one to all guards this way.
Get down and kill all who's left if any. Find a hall with a bunch of scientists and a ladder and climb it. You will see a dashboard with a "XEMONORPH STASIS" sign. Smash it and free your buddies. The door is locked, so look for a grille on the ceiling, smash it and exit the room through the vent.
You will come to the room you saw earlier from the previous one, but now it's without another alien. If you haven't freed another alien, it will be a dead end and you will have to go back and free that alien anyway. Now enter the room and go through the door which has a hole in it and follow the corridor until you arrive at a T-junction.
Turn left and kill two humans, one of them is armed. Two more scientists are hiding in rooms up the stairs. The left room is accessible, so go in and destroy the grille on the ceiling. Climb in and follow the vent until you reach a technical corridor. You can destroy another grille in the vent but that does nothing since there is also a fan blocking you way. Just follow the only path there.
Map 2[edit]
After a cut-scene you will appear in a hall with a receptionist with his back to you. He'll spot you pretty soon anyway and run away. Follow him to a neighboring room with two guards and one more scientist. From there go to the next room which you previously saw in the cut-scene. There's nothing at all, so head up the stairs and deal with two guards.
In the room destroy a grille on the ceiling, follow the vent and drop down. On your way you will hear Rykov's and Eisenberg's plans but you can't reach them anyway.
After dropping down slay a civilian and enter a technical corridor. Turn right and walk until you see an exit on the right. Now you can drop down without taking any damage, so why not to try it out? You need to reach a technical floor, it's lit with red. Go up another vent and finally you're in a room you need.
After you kill a scientist two guards will appear, so get prepared. You can see Prince in the room below. Go to the exit door and up to the vent. There is the only way to follow, so follow it and drop down. You're above the reception (or whatever). Smash the grille that is already damaged and drop down.
There are two tasty civilians if you need to restore your health. Go to the storage and you will find two more civilians. Don't be hasty, a guard will appear pretty soon. After you kill him two more guards with shotguns will run from where you entered the storage. When you've done with them, go upstairs and smash the control panel to move and drop barrels with acid.
Drop down after the box. At the lowest floor there will be a control panel for the artificial hive you need. Destroy the panel. Done! Your mates will do the rest. Now you need to escape.
You will be attacked from both corridors, so be prepared. Turn left (facing the control panel) and go to the corridor. On the left will be the open room. Go in, drop down and you will see other drones being killed by turrets. Don't waste time, rush to the safe spot under the turrets.
Go to the open door and kill two scientists. Destroy the box with a "POWER STATION" sign and go to the door which was previously shut close right in front of your nose. At first the room looks pretty harmless, but once you kill one of two scientists you will be attacked by two guards. Try to lure them closer.
Looks like a dead end. You need to smash a metal cover on the floor which at first doesn't looks smashable. Look for it in the corner, destroy the lid and drop down. You're on a technical floor. Go to the opening and you will find yourself in the central pillar. Humans on bridges are not easily reachable without taking damage, so it might be wiser just to ignore them. Your destination is a hole where a broken fan is up above.