I had embarked on a volcano for easy magma access, got the fort up and running and churning out valuables in a relatively short time. Then I got greedy, wanted to produce even more good because zomgwealth! and set about constructing auxiliary smelters and forges. For that, of course, I needed some magma to construct over. Naively presuming I had the whole pressure thing more or less worked out, I sent my miner to create a channel down into a small reservoir area, and then hack into the side of the magma tube.
First off, the miner was more or less instantly disintegrated. So much for the hasty retreat to safety I had envisioned him undertaking. The magma flowed down into the reservoir... and directly across the single z-level with a ramp which led there, then out the mining access tunnel, and into the fortress proper. I was feverishly working to establish some sort of damage-control on the situation when, quite literally, within 15 seconds of catastrophic magma containment failure, I receive the notification for a vile force of darkness entering the vicinity. Leaning back with a somewhat beleaguered smirk, I thought to myself "Ha! So they're going to try the old double jeopardy situation on me, eh? Fortunately, for once I have constructed a well-defended entrance with drawbridges and numerous lethal traps designed to ensure gratuitous goblin dismemberment!"
No sooner had the thought crossed my mind then I realized with no small amount of horror that I had probably just jinxed my fledgling fort to oblivion. Sure enough, upon closer examination of the goblins' general direction of movement, I discovered that earlier, in a fit of overzealous strip mining, I had left one single diagonal gap near the base of the volcano connected with the outside world, which my ill-intentioned neighbours had every intention of exploiting. I couldn't even send masons down to construct an impromptu perimeter, as they would always balk and return for a drink upon encountering the now-prodigious magma flow.
The goblins infiltrated my fort from the bottom and reduced the population from 80 to about 30. It was a massacre. I could only watch in dumbfounded resignation as the screams and blood and loose body parts began to fill the halls, combined with smoke and flaming madmen running about as every now and then as some unfortunate individual/pet/invader stumbled or was flung into the magma cascading magnificently down the grand central staircase. All the while (and quite coincidentally), while I watched my entire stronghold quite literally go up in flames, I had been listening to this (
http://www.youtube.com/watch?v=LeNv8zlzlV8) a rather haunting piano track I had stumbled upon earlier. It added a certain degree of epic finality to the whole debacle.
I decided at this point I'd better give it up as a bad job all around and try again elsewhere.