I've made it to Katzenstein's Lab. I go speak to Watson and defeat Firegut. Then I make note of the code to open the big metal door. The quest changes to "Open the Big Metal Door" and the arrow disappears, although there is an arrow on the quest entry.
Am I missing something here? Is there any clue to the location of the door? Is thare something obvious right in front of me? Or, do I have to wander aimlessly through the lab to find the door? I've missed obvious clues before so it could be that.