After battling a large number of Termaxian cultists and their allies last time, the party decided to retreat to the surface in order to rest, heal, and re-supply. While doing so, they considered their options for further exploration into Dwimmermount. Although they'd still barely explored much of Level 5 (and hadn't even ventured into Level 6, which was also accessible by the elevator), Brother Candor suggested they return to Level 4. For one, there was still a large gap in the center of their map of that level, which suggested they'd missed a secret door, been tricked by an illusion, or had otherwise overlooked something of importance. Second, Brother Candor reasonably argued that, after so large a melee with the Termaxians, they'd run into greater opposition from the cultists this time, possibly as soon as they exited the elevator. Rather than deal with them, they might be better served avoiding Level 5 for a while and sticking to Level 4. The others in the party agreed and so they set back out for Level 4.
Much time was spent retracing their footsteps from previous explorations of Level 4. As noted earlier, there was an obvious hole in the middle of their map of this level, one that suggested there were many rooms the entrance to which they'd not yet found. So, in hopes of finding that entrance, they went back to rooms already explored and poked around once again. This sort of activity might seem tedious -- and on some level, it is -- but it's nevertheless something I was glad to see. It meant that there really had been a point to all the mapping the party had done and also that the players were taking seriously the notion that, just because they'd visited a section of the dungeon earlier, there were still reasons to return to it later. I think this is important in running a megadungeon-centric campaign, because dungeons of this sort are never "cleared." Though the characters, as it turned out, didn't encounter any new denizens in these areas (such is the luck of the dice), they could have done so (and have in other sections), and I like to emphasize this fact.
Eventually, the party decided that, assuming there even were rooms in the hole on their map, they'd not find them by going over the same ground again. So, instead, the ventured in a different direction, one that consisted of caverns and rough-hewn chambers. There was evidence of something intelligent living in this area -- there were bones arranged into symbols or possibly warnings -- but no signs of the living things themselves. Pressing on, the rough-hewn rooms eventually started to give way to more finely carved ones, as well as a bridge that spanned a chasm of unknown depths. Filling the chasm was a silvery mist whose metallic tang suggested that it was gaseous azoth or at least an azoth-derived gas.
Crossing the bridge, the party found themselves inside an elaborate series of rooms that looked to be part of a necromantic laboratory. Room after room was filled with human and other bones, as well as alchemical apparatuses. They discovered no signs of anything living or even undead within these rooms, however, suggesting that they hadn't been used recently. The party did find multiple tall metal statues carved in the shape of human skeletons. One of these, when the party approached it, sprang to life and, with some difficulty, they were able to defeat it. The statue was guarding a room whose contents proved valuable, in the form of coins, gems, and some Chaotic clerical scrolls, which Brother Candor destroyed without a second thought.
Play ended at this point, with the assumption that we'd pick up next session without any time having passed. Generally, the party retreats at the end of most sessions, to heal, regain spells, and so forth, but, occasionally, when that seems to make no sense, they stay within the dungeon and we resume play immediately after the end of the last session. For a number of reasons, that's not my preference, but I also don't force retreats unless it makes sense and, in this case, it didn't.