This Book of Knowledge though is inside the Sancta Helena’s Church Tower and as you can guess, it requires a key.
The good thing is that by finding the said key you’ll be able to get two collectibles because next to the ability upgrade you’ll also find the Essexe Hoard Treasure Map.
But first, let’s get the ability.
Assassin’s Creed Valhalla Sancta Helena Church Ability Location
On the map below you can see that this ability is found in the northern corner of Colcestre.
You can also notice that Eivor in my case is standing in the upper right corner of the main building here.
Which, is the said church.
When you get to this location, inside the church you’ll find a locked door, and this door leads to the tower, but the only way to get inside is by finding a specific key.
How To Get Colcestre Sancta Helena Church Key
The first step here is to exit the church in question and go around it.
What you are looking for is a shelf you can move, because the shelf in question masks the entrance to a hidden room.
So basically, go around the church until you see the shelf in my screenshot below.
Behind it, as you can see is a window, that you can smash. Easy right?
So, enter the room and here you’ll find two items.
The first one is a Note of Hatred on the stone coffin, and the second one is the Sancta Helena Church Key on the chair behind the said coffin.
With the key in hand return to the door inside the church and unlock it.
Now look up and you should see a ladder. At this point, you should be inside a round chamber.
Behind you is another shelf you can move, and you should pull it until is right under the ladder; otherwise, you won’t be able to reach it.
Make sure it is in the position you can see below.
Next, climb the ladder and when you reach the first floor, look up again to spot another one.
Shoot the locker on the ladder (pictured), to pull it down.
Then head up and here you will see the Book of Knowledge on a wooden table.
Next to it is the Essexe Treasure Map (make sure you solve this puzzle as well), and the Wicked Man’s Diary you may want to read.
Easy right? That’s how you get the Assassin’s Creed Valhalla Ability inside Sancta Helena’s Church in Essexe.