Tier 1: Help the Marya Defend the Southern Barricade
The town is under assault from the Sewers. It’s your job to protect it! Your first stop will be the Southern Barricade. Fight off wave after wave of enemies until they finally stop coming.
Tier 2: Help the Marya Defend the northern Guard Post
The next stop in your quest to protect the town is the Northern Guard Post. Just like before, keep fighting off enemies until they stop coming. To help you out at this Guard Post, there is a box of grenades in the corner of the partial wall on the left hand side of the below image. It comes in handy during large waves.
Tier 3: Reach the Next Gate before the Cultists Close It
It’s time to stop the attacks at their source. Head through the marked door and enter the tunnel system under the town.
Your first challenge comes in the form of a locked gate. To get past it, you must back up a ways and blow up the wall on the left side of the tunnel. Just attack it normally for a bit and when it “dies”, it will open a hole in the wall.
Tier 4: Reach the End of the Tunnels and Seal the Main Gate
Follow a linear path until you reach the end of a long tunnel. You will have enemies come at you every 10 or so seconds, so I recommend killing them while side strafing or backpedaling towards the doorway. When you finally reach it, hit the button and enter through the stairwell on the side. Once past the steps, go into the room and up to the exit door. Congratulations, you’re done with this one.