1.Downtown - Look for the white door to your right, just after you've been attacked by the first Clicker.
2.Museum - Once you've become separated from Tess and Ellie, enter the cafe that's to the left of the room with the horse statue. The door you need is on the right as you enter.
3.The Woods - When you enter town after the woods, look for the building to your left after the second drop.
4.The Woods - After making your way through the town, you'll encounter a Clicker that detonates a trap of Bill's. Go around the corner from here and the Shiv Door will be on your left or right, depending on which way you approached it.
5.Alone and Forsaken - Enter Kingston Bookstore, then go to the second floor up. You'll find the next Shiv Door inside Rivers Cafe, to the right.
6.Alone and Forsaken - After the cut-scene, when Joel's hiding behind the taxi, look for the taxi door with a red X marked on it.
7.Financial District - Head to the back-room of the Credit Union with the Irrational Depot sign over it. The Shiv Door you're looking for is blue.
8.Escape the City - After you've met up with Sam and Henry, head down the corridor and into the stairway area. After going one flight down, look for the wooden Shiv Door right in front of you.
9.Hydroelectric Dam - There's a point in this part of the story where you need to turn a valve. The door is to the right of this valve.
10.Science Building - After you've clambered into the building via the truck, head down the corridor, then past the doors and the vending machine until you reach the end. The Shiv Door is in the furthest right-hand corner.
11.Cabin Resort - Head over the road from the petrol garage until you come to a hotel room with a missing door. Climb through the broken bathroom window and the door you're looking for is to your left.
12.Underground Tunnel - After Ellie opens the door ahead of you both, open the Shiv Door on your right before heading into the tunnel on the left.
The Firefly Lab
13.The Hospital - The final Shiv Door is located on the sixth floor of the building. Go around the right-hand corner to find it.