Among the many collectibles you can obtain in Hell is Us, some of the most unusual are the Vaults of Forbidden Knowledge. As their name suggests, they aren't exactly items, but rather storehouses filled with loot containing... a bit of everything. Actual collectibles, pieces of equipment, useful consumables... In this section of the guide, you'll find the location of every Vault, the code needed to open it and everything waiting inside.
Technically, the intended way to find and open these Vaults is to first collect Research Items that Tania can examine in the APC (this feature is unlocked as part of the story). Once you've collected enough of them, Tania will give you the Vault's approximate location and the code needed to open it.
However, if you already know where a Vault is and have its code, you can open it immediately.
This Vault in Senedra Forest is near the OMSIF camp at the top of the hill beside the APC. You probably remember the location of the Caddell Family Treasure Mystery. Head up the slope beside the APC and follow the trees marked with an X until you reach a military tent.
Go to the other side of the tent and look to the right. You'll see the entrance to a tunnel in the rock that leads directly to the Vault door. The code is shown below:
Inside, you'll find the following items:
This Vault in the Vyssa Hills is behind the waterfall, near the starting area. Once you've made some progress through the story, it will be slightly ahead and to the right of the APC. You need to pass through the tallest waterfall and follow the tunnel until you reach the panel.
Enter the following code to open the Vault:
Inside, you'll find the following items:
Head to Lake Cynon, follow the path and go down towards the field of flowers. Head east-southeast, as though you were trying to pass beneath the cliff where the lookout point with the tables is located, and you'll see a path running along the shore.
Follow this path to the cave containing the door, then enter the following code:
Inside, you'll find the following items:
From the APC on the road, head straight ahead and take the first turn south through the forest. Continue for a while until you reach a large clearing filled with ruins and a whole host of enemies.
Go around the ruins to find a bridge leading to a tower.
As you approach, you'll see a tunnel. Pass through it and you'll find the Vault entrance directly ahead. The code is as follows:
Inside, you'll find the following items:
To reach the Vault in the Acasa Marshes, you must first open the gate to Observation Outpost 08. Once you've done so, follow the path to the east and circle around to the left, staying close to the shore. Eventually, you'll reach a cave leading to the Vault door. Enter the following code to open it.
Inside, you'll find some valuable loot, including four different grade 4 weapons, which will make it easier to unlock the achievement/trophy for upgrading one weapon of each type to grade 5. You'll find the following items:
To reach the Vault in Jeljin, first take the street south of the church, leaving the enclosed yard where you obtain the Crane Keys on your right, then turn left into the fenced-off excavation area beside a save point.
Climb down the ladder and continue straight ahead until you reach the door, which you can open using the code shown below.
Inside, you'll find the following items:
Remember that there's no achievement/trophy for opening them all, but every Vault contains Relics and items tied to achievements/trophies... so yes, you'll still need to open every single one.
