An epic failure of mine is listed as a story in the Dwarf-ympics thread.
At first, there was a fort. A darkelven fort. Temperate territory, a river nearby. The people were busy, they dug an impressive underground chamber, a large watchtower above the entrance, and an extensive under-the-floor water delivery system. Yeah, right. Somehow I forgot about how U-bends generate infinite pressure. So, the fort was quickly filling, and the only relatively safe areas were the recently dug rooms, and the sealed trade depot with two melancholy elf traders and their melancholy donkeys. Seeing no way to stop the water, and being down to 3 dark elves (two stuck underground in rooms, one aboveground), then 2 dark elves (a pet jaguar of one opened the room door), then one (the guy got thirsty... he got more water than he hoped for), I decided to abandon. The top levels were only beginning to fill when I ordered the last inhabitant of the fortress to dismantle the bottom row of walls of the watchtower, that buried him under when it fell.
Then I started an adventurer. A dark outcast (drider, dark elf/giant spider crossover) Play Now! guy. He started at the remains of that fort. Considering the danger of flooding to be minimal (I remembered that the top floor where the trade depot is was not flooded yet), I steered him down into the ruined entrance under the collapsed tower. Some equipment from those traders could be handy, I thought. A short walk later, I find a very convincing tsunami heading towards me through the tunnel. Somehow the flooding accelerated in adventure mode. Oh well. I try to go back and climb out. No luck, I'm already in water and drowning. The only chance to escape is to learn to swim. I quickly wade through the water to the trade depot. It's dry in here. The traders and the donkeys are dead, but that's not the point. I spend a while working as a valve, letting some water into the room so as to learn swimming safely. After several excruciating (game) hours, the drider is a novice swimmer. I decide that a quick nap will not harm me in any way, and even help, because drowsyness decreases speed. So after a few hours of sleep, the drider wades out the door and down the tunnel. He wades, wades, he's starting to drown already, but the end of the tunnel looms ahead. Then there's a dead end. The stairs are encased in ice. After a few helpless moments of wading, the drider drowns. After a minute or two, the stairs thaw.
Need I say I never saw the water freeze for so much as an infinitessimal moment when I ran the fort? That's just my (or his) luck.