Stick to the left side of the path and go straight. You will see the device stomping on the ground which keeps antlions away. You have to get there. Follow the left path. When it's over jump on the right one.
Keep going straight. Follow the path and you'll get to the other side of the abyss.
Kill the antlions in the vicinity of the device and get down.
In the left and right tunnel there are medkits. Use them if you need to. When you're in the middle of the room the fight will begin. The zombies will show up and antlions as well. Shotgun is really helpful here. Headshots and manoeuvring are the key to success. Try to repulse the first attack and head towards a lift. It's right behind the device when looking from the side of tunnels (A).
When you're there, call the lift. Stand next to the shaft. Before the lift gets to you, you will have to repulse the second attack. This time they'll attack mainly from the roofs.
When the lift is finally there, go inside immediately and press the button. On your way up, you will still have to fight with the antlions.
At some point you will notice that the vort is coming up in other lift. When you're at the top, get to the room A. Collect the goods and wait for the vort to start up the generator.
Go straight. You will see a door blocked with tables. Use the gravity gun to remove them.
When you get to the next room, something will bang at one of the walls. Vort will tell you that it is the Guardian who is watching the larvae essence. At this point, however, you don't have to worry about him. Take the goods next to the wall and head left .
Walk straight. You will find a hole. Get down. Just follow the path and you will get to the blocked way. Remove the plank with the gravity gun (LMB or RMB) and keep going.
You will enter another tunnel. To the right you will see another entrance, enter it, but first get to the end of the tunnel and take the goods.
You will find a lift that is closed (A). You will have to unlock it. Vort will stay by the lift. You should go to the tunnel just behind it.
It will turn out that big fan is blocking it. The following film will show you how to deal with it. When it's done, keep going.
You will find another hole. Go down and straight ahead. You will fall into the water. When you swim up, you're almost at your destination. Dive into the water. Swim through the underwater tunnel and remove the web.
Kill the barnacles and head to the illuminated entrance (straight ahead and then left).