Having problems locating the AC Valhalla Londinium Bureau key? Once you've built the Hidden One's Bureau for Hytham in your settlement, he'll ask that you look out for long-forgotten Bureaus located throughout 9th century England.
One such Bureau is located in Lunden and appears to need a key to access the treasures inside, which includes one of the AC Valhalla Codex pages, as well as the wealth located there. If you're stuck trying to figure out where the Londinium Bureau is, or how to get inside, read on to find out.
Here's the AC Valhalla Londinium Bureau key location
To locate the Bureau, you'll need to head to the northeastern part of Lunden. You'll notice a lot of ruined Roman architecture here and a tall, circular wooden fence structure. Climb the wooden fence and dive into the pool below. Now, instead of climbing out, dive down under the surface of the pool and use your Odin's Sight. You should see treasure and to the left of that—still underwater—is a breakable wooden barrier. Smash through this and swim down the passage until you can surface.
If you look up and to your right, you'll notice one of those breakable walls that can only be destroyed by the explosive red pots—we'll come back to that in a second. First, grab a nickel ingot by diving underwater again beneath the suspended wooden platform around the corner. It's in a small gap containing a chest.
Now you want to climb up onto the wooden platform and jump across the building with grated windows. Pull yourself up and move to the window in the middle and you should see some red jars placed handily on the other side of that breakable wall. Use your bow to shoot them and break down that barrier.
You'll need to use the poles and ropes to climb to the now open window and once inside, you'll have access to all the goodies there, including the Codex page, the AC Valhalla Londinium Bureau key, and the Hidden One's Mask. You can use the key to unlock the door here which gives you a quick way to get back to the pool you dived into. From here, just locate the movable block opposite the wall with the three banners and move it to return outside.