The Arboria Castle Strongbox is one of the most confusing puzzles of its kind in Crimson Desert, though it's not entirely worth the effort.
Arboria Castle is located in the north, between the Hernand and Demeniss locations. The strongbox is found inside the main castle itself. To open it, you need to interact with each cylinder and pay attention to a specific number of audible clicks.
The main goal is to align all 5 cylinders so they sit at the same height in the center. You'll need to lower them until you hear the corresponding number of clicks.
You can turn up the game volume to hear the clicks more clearly.
Once all five boards are set, hover over the Strongbox Component on the right. Interact with it to rotate it to the right. This will align all the cylinders to the center.
If the mechanism doesn't trigger, check which cylinders are sitting too high, lower them, and try again. Once everything is aligned, interact with the component once more to open the strongbox and collect your item.
Inside you'll find an Equipment Manual, which can be read from your inventory but serves no practical purpose. The item is simply part of the Restarting the Elixir Factory faction quest.
As a reminder, Epic Games is set to release a Disney-published game in the style of ARC Raiders later this year.