You start your escape from this corner in the sewer:
Take the net.
Take the piece of wood. Combine with the net.
Use the net in the water to get a fork.
Go left and left.
Use the fork in the rat-hole to get a note.
Read the note
Blue 8. Grey 4. Green 6. Black 7. Orange 2.
Open the colorful safe.
The first digit is the number 1. Blue + Red = 8. 2 Is Blue + Yellow = Green = 6. 3 is Red + Yellow = Orange = 2. So code is 8 6 2
Open and you get a neon light bulb.
Go right. Then right again.
Insert the light in the black socket top left.
Turn the red knob to power the light:
You will get a code... 3374 for me. You will get a different code.
Move the tile on the floor.
Zoom in on the hole to open the trapdoor.
Use the code you saw on the wall. (Remember you will have a different code here)
Open and you will get a puzzle.
Solve the puzzle.
Hint: In the middle you will get the words SEWER 1894. The top 2 and bottom left corner will be easy... it is the rounded sewer corners. Bottom right not so clear.
When solved you will get a Green key.
Go all the way left and use the green key to open the crate.
Solve the mathematical puzzle:
C = 5 (Bottom row: C + C + C = 15 so C = 15 / 3 = 5)
C + A + C = 30, so A = 20.
C + A + B = 40, so B will be 15.
Enter the code: A = 20, B = 15, C = 05.
You will get the red key.
Go right and open the crate with the red key.
You will get a shepherd's crook from the crate.
Use the shepherd's crook to get the ladder. (Top middle area.)
Climb the ladder to escape.
Well done on a great escape.
I hope you enjoyed my walkthrough.