Book of Knowledge
When you enter the Archives through the main entrance, you can see up above in the entrance hall, that something is blocking your way up.
Go out, climb the scaffolding and shoot the big cargo down through the window (screenshot).
Now you can go back inside to the entrance hall and shoot the ladder down from there. Now you can go get the Book of Knowledge.
Grants: Rage of Helheim - Melee Ability
The chest with the Tungsten Ingot is inside the tower. Both doors are barred.
You can shoot one of the barricades from outside through the window.
Now you'll notice, that the chest is behind a weak wall.
Notice the black splatters outside? They lead to the Oil Jar down the ladder at the base of the tower...
Eboracum Bureau - 1
Gear: Hidden One's Robes
In the most southern part of Jorvik at the border to Eurvicscire is the Secret Entrance for the Eboracum Hidden One's Bureau (see map).
Climb down and dive through to the other side where you will find a big area with a flooded pool again.
With the crack in the wall - that you came from - in your back, swim all the way to the back right corner of the pool.
Here you can dive and use a passage underwater to get to the other side.
Here you can access the bureau.
There is a chest with a lock and a locked door.
The key for the locked door is on top of the shelf with the many documents next to the locked door.
Unlock the door and loot the chest.
Reward: Hidden One's Robes.
Eboracum Bureau - 2
After you unlocked the office for the previous wealth collectible at the Eboracum Bureau, grab the key from the table.
Now you can unlock the chest
Enter the Forseti's Rest Building.
Behind the diagonal chessboard pattern wall there's a stone shelf you can move. The screenshot shows the entrance point.
Pull the shelf towards you so you can access a room at ground level that hides a key under a wooden box.
Smash the box, collect the key.
Now use the stone shelf to climb one level up to the chest.
Reward: Fyrd Axe - Bearded Axe
The chest inside a cultist's house west of Councillor's House.
The door is barred. Either enter through an open window or through the roof (smash wood).
The chest is locked with 3 locks.
The keys can be found at the location of 3 Cursed Symbols in Eurvicscire:
The key is on top of the tower next to the Cursed Symbol.
The key is down in the Ritual Circle tomb behind the locked door.
The door key is in the frozen lake. Smash one of the 2 light weak ice patches to dive for it.
Loot the body in the unlocked room to get the key for the chest in Jorvik.
The key is at the base of the big tree where the Cursed Symbol is in.
The chest at Jorvik Theatre is behind a stone weak wall and locked up.
First, locate the oil jars. They are up the stairs in the southeast.
The Key is right below the oil jars in a room that is blocked by a wooden barricade.
Pick up the key, then an oil jar to destroy the weak wall (see screenshot).
Once inside the hidden room, move away the stone shelf to get access to the key locked room.
Use the key to get to the chest.
Reward: Aella's Bardiche - 2 Hand Axe
Multangular Tower - 1
The access for the Tungsten Ingot chest is at the bottom of Multangular Tower.
Follow the corridor until you get to the first room, where two hostiles are looking at a weak wall.
Fortunately there are some oil jars in front of it so you can get rid of the men and the wall.
Follow a passage in and move away a stone shelf.
Shoot down the ladder that leads to another weak wall. The Wealth Chest is behind it.
There is a wooden wall you can destroy with oil jars behind it. Careful! Snakes.
Now, move the shelf just enough towards the ladder so you can use the platform with the staircase to parcour onto the shelf.
Pickup an oil jar and get on the shelf. From here you can throw the oil jar onto the weak wall.
Needs a couple of tries!
Multangular Tower - 2
Exit the room. In this corridor is another weak wall you can blow up with an oil jar.
Do so and enter it.
The next room is full of scaffolding and another set of oil jars.
Use the scaffolding and rope to parcour an oil jar to the next weak wall.
Once open, go through and enter the water.
Dive towards the grid window, underneath and through to the next room.
Here's another set of oil jars and a shelf you have to move.
Move the shelf and use the oil jar to destroy the weak wall. This gives you access to the Gear Chest.
Reward: Sagittarius Bow
The chest is at ground floor where the altar is.
It's at the base level of the Trade Depot.
You can access from the roof.
Reward: Spinning Death - Flail