In the storage room in the corridor south of the parcour, there is a locked chest under a bunch of packages, with the key under a barrel (IIRC) by the northern door. Perhaps you missed the chest there?
forge <span class='standouttext'>Spoiler : </span><span class='spoiler'>In one of the rooms in the pit level you could have found a book explaining how to make gunpowder, though you don't actually need the book. You need a coal barrel (from Fergus' room, first level) + salt barrel (citadel kitchen), then to this mixture add sulphur from the citadel medic's room. Drag and drop the resulting bomb onto the forge.</span>
