Well the adventure went reasonably well. The after climbing down the ladder the half party finds itself in a room filled with periwinkle mist. They defeat the ogre which materializes out of it and add the paladin which materializes to the party (had to add the new player somehow). They move on to find in the next room to find a kobold wearing welder's goggles and a reptilian beast with glowing periwinkle eyes. The kobold turns to gas and flees sicking the beast on the party. The discovers much to its horror that the gaze of this beast turns people into periwinkle mist, but only the druid misses enough saving throws to be fully affected. They find several bottles of periwinkle mist carefully labeled things like "White Dragon" and "Frost Giant". They put the druid in an empty one. They progress on to the next room which has one door heavily guarded by a balista, barred from this side with a lighting bolt projector in front of it. The other door is just shut although closer inspection reveals that it is barred from the other side. The thief uses his tools to unbar the door. On opening the door they find a chamber with four iron cells on the left and a carriage equiped with four dragon headed nozzles on the right. In back is the kobold with welders glasses and another kobold with a whip. The party decides to talk, once the kobolds explain about the four nightmares behind the iron doors, the party decides to go a different way. They talk the kobold with welders glasses into disarming the traps in the previous room exit through the formally heavily trapped door into the great underway and reunite with the rest of the party sleeping in the kobold camp above. They retreat to a hidden spot and take a long rest (there is some stupidity with a captured kobold which I will not go into). They are horrified to find on their return to the underway a drow army storming through (guess they weren't the only ones interested in finding out how the traps for the door worked).
Final Battle Mat
Original keyed sketch
P.S. Although the players prudently exited before reaching the lava pool, I am bit disappointed not to see how 4th levels deal with lava.