After going through the only door on the Platform, you will be faced with a long stairwell going down. Turn right and head to the end of the hall and use the double doors.
Turn left and run past the two Pendulums, and go through the blue door on the right wall.
Run straight until you see a blue door on your right, take it into a narrow hallway containing two Numb Bodys, take your first left and go through the door at the end of the hall to find a store room.
This Store room contains the Maul, to the left of it is the Underpass Map on the wall. This will make navigation much easier! When you’re ready, head out the door to the South.
This hall has a large and small Numb Body in it. If you follow the hall around the corner at the Western most door, there will be two boxes of Shotgun Shells on an oil drum. First you’ll need to take the blue door on the west side of the hall. Inside this corridor you can find two Health Drinks and Beef Jerky. Investigate the wine rack to find an empty Wine Bottle.
Head back out the door into the last hallway. This time you’ll want to take the door on the East side. A few more Numb Bodys may spawn in the hall before entering the big white door.
This next hall will hold two or more Pendulums. You can easily ignore them and go through the blue door on the North Wall about half way down the hall. It will take you to a long and well lit hallway.
At the end of the long hall way is a dark area. Turn Right to find the only door to the next area hall.
This hall contains two rooms on the West side of the hall, and a room at the Southernmost wall. The room to the South has nothing but monsters inside. You’ll find a large Numb Body and two small Pendulums. Now, head to the two rooms on the Western Wall. The first room you should go to is the one on the bottom (South).
It would seem this room used to be an Office. You can find two Health Drinks, Handgun Bullets, Shotgun Shells, and a Save Symbol. The most important thing in this room is to the right of the Save Symbol. Look for the large grey cylinder. Investigate it and you will realize that it is full of oil. Use the Wine Bottle to fill it up with Kerosene. You’ll know have the Oil-filled Bottle. Now, leave the room and go to the next room nearby. A few more Numb Bodys should spawn in the hall.
This room houses a large generator. Next to it is a ladder down into a room filled with water. Obviously, you won’t be able to go down into the water, but that’s why we have the Oil-filled Bottle. Use the bottle on the hole in the Generator to fill it up, then use the small keypad to the right. This keypad is a hoist on / off switch. Switch it on to empty the water in the room beneath you.
Climb down the ladder to the room below and head up the stairs to find a door to the next area.
Go straight (East) and you will end up in a corridor that goes South. At the end of the long sewer, you’ll find a blue door on the West side. Enter the door and head East until you reach a Garbage Room. Inside the room you will find an Ampule on a shelf and a Dryer on a chair. Now return to the Open Sewer hallway, and use the white door across the hall.
This small T-shaped hall will contain two Numb Bodys. Move on and enter the door to the left (North). Inside this door is a Security Office. This office has a Save Symbol on the floor, and a Health Drink on the desk.
When you’re ready, go through the door on the other side of the room. You may want to read the warning on the floor before venturing on. There will be a sewer monster in this room. Do not walk on to the platform!
Unlock Gold and Silver Pipes
Before using the Dryer on the outlet, examine the pool. Unless you have it equipped as a weapon, you will be prompted to throw the Steel Pipe in the water. If you do so, you will be asked three questions. Answer them honestly, and you will receive the Gold and Silver Pipes as a reward, as well as getting the Steel Pipe back.
There is an outlet on the wall beside the door you just came through. Use the Dryer from your Items here to kill the sewer monster. Now you can cross the platform and go through the bloodied door.
Keep heading South through the next hall and you will end up in the open sewer again with two Pendulums. Follow the walkway around until you find a long hallway with a blue door at the end. Go down the steps and back up to find yourself in a large room with a ladder at the top of a flight of stairs. Use the ladder to leave the Sewers and enter the Construction Site.