The landscape was already a mess. More specifically, the entire left side of the 4:4 embark.
No, it wasn't collapsed.
Not yet. Instead, it was flooded. Apparently, Mother Nature decided to have the river's edges cut out on a waterfall, completely flooding the entirety of the lower plains.
Because of this... hilarious cascading effect, there were no fewer than 5 additional waterfall generators at any given time.
After a full season of realizing the river wouldn't freeze over, I decided to dam it by using screw pumps.
When that failed, I simply dug a 4x4 staircase, going down 50 z levels. This stopped the rushing waters for a few minutes, allowing me to block it off once and for all. Now I just needed to wait for the water to evaporate.
But it just wouldn't stop raining. Thus, the new swamp never truly left.
After that FUN!! experience, I needed to find more sources of FUN!!. Slithering about, I discovered I had a dwarf, Solon, who was a cook... with Legendary level fighting skills.
Quickly dubbing them "Not A Vampire", I assigned them as my militia captain and just kinda stalked them for awhile. Weirdly enough, their sole activity was to pray to some deity of music and wealth. They would go days without respite, just kneeling in the middle of the common area.
And now... the moment you've been waiting for.
It was quite sudden, really. Couldn't even get pictures because I was panic-force-quitting the window the entire time.
Here's what my Announcement list said.
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"Something has collapsed underground!"
"Dwarf McUrst has cancelled task: Dangerous Terrain." x 42, all at once.
"Horrible screams can be heard from below!"
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Somehow, for some unknown reason, all stone just... disappeared. In an instant, the surface world fell 100+ z levels, somehow cushioning a select few dwarves from a grisly fate.
Roughly 30 demons rushed to ravage the catatonic survivors as I just force-quit the game.
The Pillar of The World had collapsed on me.