This page of The Last of Us game guide contains a walkthrough of the Underground Tunnel as part of the Bus Depot chapter. In the title tunnel there is a very large group of monsters, including clickers and a bloater. In our walkthrough you will also find a map that should help you avoid most of the monsters. The rest of the stage is mainly exploration and a scene during which Ellie is saved.
Once you get underground, keep to the wall on the right.
Start of the fight
Suggested player route
Suggested kill areas
If you move about silently here, you will manage to avoid the majority of the enemies here.
Still, one of the zombies will step in your way. Sneak up to the monster and strangle it.
Another enemy that you will have to kill is waiting in the room to the right. After this one is dead, you can go left and leave.
Take a few steps to the right and sneak up onto the truck on the left. You can climb onto it over the cab.
Once at the other side, keep to the left wall. This way you will reach two bloaters. To move forward, you need to draw their attention away with a brick or a bottle.
A bit ahead, there is a clocker waiting for you. Stab it with your knife and give Ellie a boost onto the vehicle that is blocking the way.
The girl will throw down crate for you to climb over to the roof.
Keep running ahead until you reach a fire truck. You need to dive under the truck, climb up at the other side and throw down a ladder for Ellie to climb onto.
As you proceed ahead, you will reach a closed gate. Give the girl a boost to the hole on the left and save her from a clicker. You need to shoot at the monster through the lops in the fence.
A moment later, Ellie will open the gate.
After you reach an abandoned corridor, check out the door to the right. You can open it with the knife and collect many useful items.
As you run ahead, you will reach a flooded part of the metro. Jump into the water and swim into the room to the right. By keeping to the right, you should soon resurface.
Climb to a higher floor there and get to the other side of the location through the ventilation shaft.
You will find a wooden palette there to transport Ellie with across the water.
The girl will then slide down the ladder, which you need to climb. Unfortunately, the ladder will break under your weight. Collect the destroyed item and climb onto the place where you found the palette, over the ladder.
You can now transport the ladder up to the broken footbridge. Use the ladder as a footbridge and go ahead.
Keep jumping over from one vehicle to another in the big tunnel, until Joel falls down into the water.
You will then have to grab onto barriers to the right to get to the exit (triangle).
When you get washed down again, press L3 and start pressing the triangle again. A moment later, you will get underwater.
To finish this stage, swim ahead and take the drowning Ellie with you. As soon as you reach the surface, you will see a longer cutscene.