I haven't found the key I need to access what I assume is the boss area yet but I did stumble my way into this poisonous area where everything is poison and there are corpses hanging from the ceiling and also more poison and then I died XD
So I made my way back to that suspicious part of the other route - examining the door (as you would in ST1) doesn't do anything but if you hit it the whole thing comes crashing down! :O
Swapped out my weapon for a baselard I'd picked up earlier and cleared out the insects - at one end of the corridor are a few husks of something, and at the other is a gap that seems to lead further in but I can't get through...
I was able to break through this crack in the wall and do a little exploring but the cave system seemed to end soon after, even if I can still hear monsters nearby. I might pop back here in a bit.