So, I've hit my height limit for my tower, as my upper ceiling was +10 Z. You cannot build walls on the highest level, sadly, so I'm going to make this a sort of outdoor temple. However, on level 9 I've set up preparations for a dwarven drop system, which will drop a soldier (or several) from the top of the tower, all the way to the surface, landing safely upon a chained dog or other creature, at which point the Fun begins and the dwarves fight whatever is out there.
After a few moments, I decided this wasn't nearly dwarfy enough.
Project Armok's Thunder, which shall be repeated when I eventually make a new world and a higher ceiling, will involve an entire barracks that's supporting by an overhang. Unique to this barracks is that it shall have no ceiling, and very tightly controlled training positions, perhaps done via burrows or otherwise via the forbidden internal door trick. When triggered, the system will drop the dwarves down upon waiting living cushions - as well as the entire barracks itself. That's correct, the entire barracks will descend the distance to the ground, which should create a plume of dust sufficient to toss any would-be invader clear across the map, providing the drop troops enough time to prepare and meet them face-on.
The prototype, made within my shorter tower, will drop a pair of weights down, instead of an entire barracks. The specifics of design shall be revealed upon first firing, for which will will elect Urist McUseless to perform the first live firing. That's correct, HelpedFountains is animal-friendly! Except for the animals having armored soldiers dropped upon them. Upon successful testing, the system shall be expanded to allow orbital drops into the caverns themselves, through a narrow drop tube. This promises to be an exhilarating 50+ level drop!