So, I've been building fortresses for a while now with an Elven-depot-death-trap (enclosed room with the trade depot, above it is a floor hatch in a chamber filled with water via an aqueduct or screw pump system, and I've got a lever that closes floodgates and opens the hatch, resulting in elf bones and more cloth than I'll need anytime soon), and decided to scale it up for my latest fortress: in front of my fortress entrance, I built a largish maze (not branching or anything, just designed to maximize the time it takes orcish hordes to proceed through it) and built a water chamber on top of it.
Actually, I got a little carried away and turned the water chamber into a 15 z-level hollow pyramid, filled at the top by an aqueduct that I sealed off once the pyramid was full. And then I waited.
I'm pretty sure that I've done these water death traps on maps that froze before, so I'm not entirely certain why what ensued, ensued, unless my memory is incorrect.
Come winter, I noticed that the entire pyramid had frozen solid. "Cool", I thought, trying to remember whether I had modded orcs to not show up in winter or not and whether I was about to get pwned (they didn't attack that winter, anyway), "but what happened to the floor hatch?" It didn't look like I had originally installed it. It sort of looked...de-constructed. I assumed water freezing made the floor hatch look that way, and didn't attempt to check if it was, in fact, deconstructed.
Come spring, I was busy managing stockpiles when I started noticing some spam about canceling tasks due to dangerous terrain. The pyramid had melted, and due to a poor decision on my part on how to have floodgates set when the fortress was not under siege, the entire volume of water was pouring straight down my central shaft. I frantically ordered my dwarfs to pull the lever to seal the hatch, and when that failed (since it was now deconstructed), I ordered them to set the floodgates in a less fatal configuration, but all for naught. My last two surviving dorfs were sleeping in their rooms at the time, at the very bottom of the fortress, with a LOT of water outside their doors and guaranteed death if they opened them. I abandoned. I'm coming back with an adventurer later.
1.) Losing is fun. This was my first truly spectacular defeat, however, aside from tunneling into the ocean, which was just a mistake.
2.) Is freezing supposed to do that?