I did not pick up the area map because I entered the dungeon from Gadd's Encampment rather than from the entrance in Arbor Bay, if that matters... which means that I am much closer to the stairs to level two than to the area map, so I have not gone all the way back to get it. I have looked at the dungeon maps on wiki and they do not say anything about a closed door, a trigger, or anything else that should be blocking my way.
ps: Well, it certainly is not picking up the area map that opens the door - I just picked it up and the door is still closed. Very puzzled here. Has anyone else gotten to the second level after entering from Gadd's Encampment? If so, did you have to do anything to open the door that grants access to the area with the dungeon lock and the stairs to the second level?
pps: okay, I have now killed the second "semi-boss" Cursed Brigand on the first level as well as his group, and still the door is closed. I've almost cleared the entire level, and there are no braziers to light or other apparent triggers anywhere on the level. There isn't any mention of a closed door on the first level in any other thread on this topic or on the wiki. Has anyone else run into this or have any suggestions? I'm about to give up for the night but I would appreciate any leads in case I am ever inclined to try it again. Many thanks in advance.