If you want to have some framerate-frying Fun, here's what I'd suggest.
Build an Orbital Magma Cannon. Basically, floor off the entire map about 5 Z-levels above the highest single point, all from a single massive tower somewhere on the map in which you are pumping up MAGMA, powered a windmill farm so vast that whole flocks of birds fly into it and turn into chum.
Now, for an orbital magma cannon, what you do is have a hatch every 5 or so squares, on both X and Y axis, so you have a grid of squares. About a 5x5 section of hatches (so, 25x25 total squares or so) would be connected to a single lever somewhere in your fortress. On the ground levels of your map, you place notes with targeting coordinates, and you apply the same notes to your lever room.
Basically, what you want is a 5 or 10 z-tall reservoir of MAGMA above the map, sitting pretty, so that when you [P]ull the Lever, a shower of magma rains down on the grid coordinates of your choice, causing much Fun for anyone caught in the blast radius. At least, that's how it works normally; you get invaders, look up their coordinates and pour molten !!Fun!! from the skies onto them.
But in this case, since you want some dramatic !!Fun!! for the whole !!Fortress!!, I'd suggest you disassemble all your doors and floodgates and hatch covers and rain fire down on the whole freaking glacier. If you set up the pumps right (by 'right' I mean 'can't be turned off' and immediately disassemble your targeting room, there'll be no stopping the rain of magma. You'll have all the !!Fun!! you could ask for.
Or, you know, if Operation:Fuck the World is too much damn trouble to unleash these days, you could just draft everybody as a wrestler, dig down into the cotton candy and find a drinking straw...