In my latest fort I created a square room, 7 levels tall. Each level had the middle 5x5 mined out, leaving an empty shaft the entire way down. Outside the mined shaft I left a little room so dwarves could walk around the shaft and, most importantly, place items.
At the top I built a retracting bridge in the open space. At the bottom, I used gold plates and kolenite (red stone?) to create a target.
Starting on the second floor from the bottom, I lined the edge of the shaft with coffins. As the true heroes of my fortress die, I entomb them in these coffins and sarcophagus, with the earliest heroes being at the bottom, and the latest heroes at the top. Thus, the history of my fortress lies entombed within this Fall of Memory.
The bottom floor is left empty except for the target painted on the ground, so the falling dwarves may focus all their efforts on hitting the bullseye.
Dwarfs come from all over the world in order pay pilgrimage to the forgotten heroes of the land - by throwing themselves out into the Fall of Memory - and are honored to be able to view the coffins and engravings of true masters and warriors as they fall to the bottom.
On a technical note - 5-7 levels isn't exactly enough to kill all dwarves instantly. Most, but not all. I ended up with quite a few (considering the numbers I threw off that thing - stupid migrants) who managed to stay alive for a while - this was great practice for my medical dwarves, who quickly gained all sorts of useful skills.
I didn't get this set up until too late - and ended up tantrum spiraling due to an ambush + some of the people I threw off this thing. So in the end, I just drafted everyone I could and kept throwing them down the Fall of Memory until someone went into a tantrum and broke the bridge.
Still, my reclaim force will have an amazing pile of bodies to sort through.
I'll write a more story based description for this later in the other boards.