After using the stairs you will reach the underground place. Again use the stairs to reach the circular area. On the right side, you will see the forge. Upgrade your weapons if you want. Use the stair until you reach the bottom. After reaching there you will see a glimpse through the video.
Follow the Red Pipes:
Use the GRP glove to lift up the box and place it near the wall and climb up. Open the chest to get the materials. Use the vent to reach the sewers. Go to the right side and use the axle to open the vent path. After crossing the vent go to the left side by crawling. You will see a big zombie kills the guard. Go to the left side and reach the open area where you will again see a glimpse of the video.
Go to the left side of the vent and get out. Now you need to get a fuse to turn on the switch. Get the recording of the officer. You will be immediately attacked by the crawling zombie and left instantly. You also have to find another fuse. Get the fuse and activate the switch.
Kill the poison zombie and use the fuse to activate the second Switch which will activate the power. Follow the path by the pipes and use the vent to reach the Access Hall. Again follow through the pipes and use the stair to reach the bottom. Use the Axle to the left side to open the event and reach the room where you will see a Forge from there you can upgrade your weapons if you want. Use the axle while using it you will be attacked by multiple worms.
Open the Gate and follow Red Pipe lines
Open the gate and follow the path. Use the vent and move forward by the pipes. Use the stair to reach upward. Kill some zombies and move to the right side to open the gate. But first, you need to find the fuse. Use the stairs to the left side to reach another switch and take the fuse. You will be attacked by some zombies kill them and use the fuse to open the gate. Go to the left side to reach the open where you will see a glimpse of the holographic video. In which he tells about the code.
Get the code from the guard:
Go to the left side by opening the gate. Follow the path until you reach the area and got attacked by the zombie which will convert him to the other form. After killing the zombie get the chip from the guard and also the recording of the guard. Reach back to the console and activate the code. After activating the code purge cycle will be initiated.
You will be immediately attacked by the crawling zombie. After that, you will be attacked by multiple zombies. Kill them and move back use the switch to activate the ladder control. This will make a path to the ladder. Go upwards by using the ladder. And go down Jacob closed the ladder top before he got attacked by the crawling zombie.
Get to Access Hall F813
Follow the tunnel and instantly water is released. Which will push you down the tunnel. Save yourself from the object in the way. During this, you will be attacked by the zombie instantly which will jump on you. After killing him you will fall from the tunnel but save yourself by hanging with the chain. Climb up by using the chain. Get the healing from the medic box and move to the left side by using the gate. Kill some zombies and move to the left by opening the gate. Use the shiv to open the gate. Follow the path and you will see an unlocked door.
Go behind and use the vent to move forward. You will reach an underground place, clear the area and go to the left by the stairs where you will be attacked by the worm. After killing the worm go to the right side and use the stairs to go upward. Follow the path by using multiple doors which will be located in front of each other until you reach the Access Hall F813. Follow the path and open the gate to the Habitat Dome.
Use the lift to go down. Elias will ask you to go to the security station inside the Oxygen Processing. Go and enter inside through the door. After entering inside you will see a glimpse of the video.
Get the code from the guard:
Now you need to get the code to activate the console. You can also upgrade your weapon from the forge. Go to the left side by following the foggy area. Kill some zombies and search the area around for the key. Crawl and follow the path. Find a fuse to open the gate. Get the fuse from the second switch and use the switch to open the gate. Go to the right side and climb up from the box and use the vent and reach the Guard. Get the security code chip from his neck and also the audio recording.
Use the code on the control panel. And tell the info to Elias he will tell you to get to the catwalk.
Reach the Utility Hatch:
Follow the path through the botanical and move forward within the pipes. On the way get the recording from the left side of the box. Go back and get outside by using the gate to the right side. Dismantle the robot by shooting his neck. Go to the opposite side of the circular and open the gate to enter. You will see a locked door use the shiv to open the door. Kill the zombies in the Tram Depot Entrance area. Go to the left side and open the gate and use the stairs to reach the underground.
Look for the Fallen Walkway:
Now you have to look for the walkway. Reach the circular area where you will be attacked by multiple zombies. Kill them by throwing them into propellers. After killing them you will be called by Elias. You will see Elias on the wall. Climb to reach Elias and Jacob is attacked by the zombie but Jacob will throw him away by kicking with the help of Elias. You got to the entrance and Elias gives you the suit to wear. After that Jacob asks Elias about what he is into. Then he tells some back story. During the talk, you will see Capt. Pull the trigger of the door which will push you outside that area.