Find a way out of The Tunnels
Follow the path down until you reach the trains, then throw a brick or a bottle and wait for the clickers to take out the WLF. Once the enemies have been taken out, head to the end of the path and quickly get inside the crashed train.
Here you'll want to go to the end of the train to find some Supplements and an Artefact, then exit the train and head to the end of the tunnel to find a Trading Card underneath a train. Go into the room ahead and climb the ladder, then go into the room on the right to find some Scrap and a Workbench.
Grab the rope from the floor and throw it over the pipe, then swing across to the raised area and go through the door on the right. Collect the Supplements from the floor, then crawl through the vent and drop down on the right to face some Shamblers. In order to take them down you'll want to set some Trap Mines and then shoot them in the head with the shotgun or Revolver.
Once all the enemies have been dealt with, go through the shutter at the back left, then head through the first door on the right. Here you'll want to crawl behind the fenced area to find a Trading Card on the desk, then go into the room on the right to find an Artefact by the microwave, another in the cola machine, and a final one on the desk. Before leaving, go over to the door on the left and open it up with the code found on the can 15243.
Exit the room and head, drop down into another large room and take out the two Shamblers using the same method as before, then head to the right of the room and go through the door to a room full of crashed trains. Here you'll want to go through the train at the back and then take two lefts to crawl under it and find a Trading Card.
Finally, climb on top of the train via the box and then make your way into the train on the right, but before proceeding down, look to your right to find an Artefact pinned to the wall. Go down the ramp and help Dina up and wait for her to throw something to allow you to climb up, now follow the path down and you'll view a scene.
Escape the Hoard
After the cutscene you'll want to follow Dina until you exit the Tunnels and then you'll enter another cutscene.