When you're there, the vort will join you. Before moving on, collect the goods from the crates. You can find them on the boards. It's good to get them with the gravity gun. Afterwards, go to the fence. When you're close enough, the zombies will stand up. Before you destroy the planks blocking your way, kill all the zombies.
Go inside and head right. Take the goods from a locker and turn left. The zombie will jump out at you. Step back and kill it with a little help from vort.
After killing it, go straight. Take the goods from the crates which you can see on the upper screenshot. You will get to some kind of a lift. To go down you will have to put something heavy on it. Use the gravity gun to do so. Then the lift will move down. Remember to jump on it before it's too low. Mind the crates with goods (A) when going down.
When your there, go straight. Be ready to face some zombies. You will get to a room with a blocked lift. You have to get to the control room. The arrow on the screen shows the entrance.
When you're there, press the action key to move the lever controlling the lift, and take all the goods.
Get back to the lift and look at the things on it. There are some iron bars and barrels. Start taking off the objects and the lift will move.
Jump on the lift. When you're up, the zombies will attack you. Kill them all.
Then go to the place with a valve and press the action key. The vort will join you again.
The vort will start up the power generator and you will be able to keep moving. You will get to the trollies standing on the verge of the abyss. There are some crates with goods in them. There are 2 ways of getting the crates. The first one is jumping inside, collecting the goods and jumping outside. The other one is getting the crates from the trollies with the gravity gun.
Keep going straight and you will get to the blockade. There will be some zombies but you will hear antlions too. These will be acid-antlions just above your head. First of all remove the planks and move on a bit. The trolley will start going towards you and make some mess. Then kill the zombies and keep going.
You should go backwards, pointing the gun above. There will be acid-antlions. If you're fast enough, they won't manage to hurt you.
Keep moving and after a while vort will say that you have to find another way. Get to a ladder.
Climb up and go straight. You will find some kind of container and a hole underneath. Use the gravity gun to swing it (LMB). When the hole is no longer blocked, jump in.
You will land on a trolley that will immediately start moving. You will end up in the water. Swim up and get to a ladder.
At the top, the vort will join you. To the left there will be a tunnel leading to the caves. Go inside.