The Dunwall Sewers area doesn’t have a lot of enemies, instead it’s filled with traps and secret areas. This guide explains how to pass all the guards non-lethally, avoid the traps and find all the secrets:
At the end of this post is a video with a visual version of this guide.
The first secret area is just after you go through the first door you have to open with a winch:
Go to the right and stay on the walkway up top and you will easily find it. There is some loot there but not much else. Next you have to get past some rats that will kill you if you jump down to their level:
Just follow the right side of the cave by platforming on the containers and rocks until you are out of line of sight of the rats. You can safely jump down and get to the middle platform. To distract the rats take the corpses and throw them down to the rats. They have to be in line of sight of the rats, otherwise they won’t go for them. I suggest you put one down towards the entrance to the cave and one opposite the rats so that they are distracted for as long as possible. Once they are eating the corpses jump down and turn the wheel to raise the gate.
Next you will find a chain you have to climb up:
Once you are up top there is a lot of loot, a secret area and a number of traps. First of all jump into the water below and turn around. There is a corpse with some coins on it. There is also some loot on the platform you jump onto after climbing the chain. If you look into the cave up and to the right is a walkway. Jump up to it and go into the side cave. This is the second secret area, you can enter it down the bottom but there is a trap there. Jump down and loot the machine to take the arrows from it (be sure to take the rest of the loot too).
Afterwards jump back up to the platform. Once you reach the end of the side cave turn right and jump over the pipe. There is another machine connected to a trip wire on the chair on the platform. That trip wire is on the walkway to the equipment you are supposed to find.
Next there is a safe, I have already written a guide for finding the combination and opening the safe.
The last big cave you run into has 4 enemies in it (and another secret area):
Pick of the guards one by one from behind. If you throw the unconscious guards into the water they will drown. I also kept bashing their head in when I put the down near a wall, so be careful with that too. The last 2 guards are best taken out from the pipes above.
The secret is on the right side of the big cave with the sewers in it. Next to the wall are two pipes on top of each other:
That is the end of the sewers. I didn’t find any more secrets, but if you did be sure to let me know in the comments. Here is my final chapter summary: