There are several locked doors and buildings in Assassin’s Creed Valhalla. Normally, a higher level enemy may have it on their person, forcing you to take them out to secure it. Other times, you need to look around the area to find it. At Brisleah Farm, underneath it, there’s a locked door with some resources behind it that you can secure, but you need the key.
You’ll likely encounter this resource while investigating East Anglia. There’s a mission that’s apart of the Legend of Beowulf quest, and you’ll spend a little bit of time here. Once you wrap up the quest, you can find the resource inside of a farmhouse, underneath the floorboards. You can break those boards using your weapon or your bow.
After finding the door, the next part is to find the key. Luckily, it’s not too far by, and you won’t have to use Eivor’s raven to find it. If you use your Odin’s Sight, you can locate it close to the church’s front. It’ll be on the ground, in the hand that’s been cut off from the rest of the body. It’s about 60 meters away from the resource.
You can return to the resource, unlock the door, and obtain your loot. The item will be nickel ingots and titanium.