The Duke:
The Duke blinks at the lady and as she darts off he laughs like a kid and then bursts after her his massive bulk needing a little time to get to speed and it also means he has a hard time comming to a halt once though and he almost squishes the lady.
The last two areas were quick to light up once either of the two humanoids enter it, and this new area is no exception. It is a sort of stairway-- the stairs broad and easy to descend. It leads downward for about 150 feet, and then seems to turn left, although that may be to double back on itself.
There seems to be no way to open the door behind them again, so since there is nowhere else to go, The Duke and The Lady descend the stairs.
The stairs take them down oh... perhaps six, seven stories? At least it's easy-- downhill all the way... The lights overhead continue to light up as they travel...
Finally, the stairway opens onto... a large cavern. Half the ceiling and walls are metal flat stone. Half of it seems like natural rough bedrock.
Glowing, bioluminencent moss and mushrooms grow down here, lighting up areas where the ceiling overhead stops glowing.
There are many moths fluttering from fungus to fungus...
...The cavern floor slopes very gently downward. At the far end of the cavern is a very large tunnel that bends off to the right...