The name of this sewer can be deceiving. The entrance and exit hatches aren't found near Kvasir's Lab but look over at it.
It's best known as one of the Rocket Launcher locations in the game (confirmed on all difficulties), the other being the Dead City. The Rocket Launcher will be on the stairs approaching the exit. It's rather small lying on the stairs and easy to overlook.
When heading past the Watch Tower and on the way to the Authority Prison (also on the Northern Express route for the Stanley Express), the player will see the Kvasir's Lab on their left. Where the cliff ends, nestled between the cliff and the wall is the entrance to the sewers. If the player looks out over the cliff, it should be lined up with the balloon bridge used to get into the lab.
Upon entering the sewer, you will be placed in a small room. Walking forward will trigger a Club Mutant. As with all the sewers, the Combat Shotgun is advised. Kill it, and loot the corpse on the ground. Progress towards the stairs from here. Note that walking up the stairs will result in a firefight against several mutant variants, so be ready. Once you've cleared out the room, head left into a slightly larger room. In here, loot the corpse on the floor. And progress.
Head down the stairs, into a room nearly identical to the one from the beginning of the sewer. Loot the corpse at the end of the room. Note that three mutants will ambush you once you reach this part of the room. Take them out, and head through the door.
From there, you will be placed in a large tunnel-like area. Head right, until you reach a small platform. This platform will lead players to the exit.
- It is the only sewer that features an obtainable weapon.