Off cave with stalactites found room with sideways-falling rain. Nowhere for a tower to be.Down the hall, Parna found traps in a pair of alcoves. Pesky mephit set one off behind us - big falling pillar, and when I say big, mean really overboard even by dwarven trap standards. Diagram in second alcove hinted tower might be on top of second pillar - no tower, but a note saying there was something in rain room.
Further on, found a sort of key as to which six of nine key-traps were in use. Found symbol for one of two remaining on antechamber floor next door - in room beyond was big one of sound-loudening stone disks, and another one hidden in ceiling. Went and coordinated banging on two smaller disks (had found another) and the sound got loud enough to break the disks, revealing box with crystal tower.
Also unpleasant whining noise that did damage, and it would get in people's mouths and then go off again if they opened their mouth. Eventually got it shut back in the room.
Back in rain room went and stood there long enough (had to stand there to turn it on) for rain to wash mud off back wall, revealing map. Did the dwarven happy dance (very subtle, done entirely with nostrils and fingertips) and went to final - marked - key location. Turned out to be invisible in the middle of a well, locked in a impenetrable skin that came off when we plugged the symbols for the keys we had found into it. Nice smoky quartz.
Went back to tell the cloud guy we had the keys and were heading for the center; he decided not to come with given dangers of Changing Ways.
In center found a big room with big air-machine thing in the middle - put keys into slots, whole thing activated, major mechanical action kicked in, pillars dropping into floor, whole machine splitting in half to reveal impenetrable-skin pillar in middle, Siarran guys in full plate (or Siarran full plate sans guys) dropping down on pillars and stabbing Parna.
There's always a final guard, of course.