My group is called the "crypt of infamy" in my new, name-themed fortress, so I'm going to have to be looking at this thread a lot for ideas.
I've started by refusing to slab a dwarf I accidentally drowned. I now have a sealed, underwater part of my fortress with bodies in on the first level, as well as a crypt in the stone layer with a complex spiral pattern. Apart from piles of dead bodies and pits for FBs, any other ways to make it "Infamous", do you think?
That is an excellent name for a megaproject. What I recommend is making the crypts utterly inhospitable to all forms of life, including your own, and ever growing. So make the crypts labyrinth style, with many paths branching off each section, and once a section is filled with bodies, place a trap of some kind that will murder your own dwarves as well. Fill areas with undead, put crushing or dropping bridges linked to pressure pads, have spikes on repeat with an infinite minecart or water repeater, stick a deadly FB or five in a pit, or just running around, have drops into pits filled with snakes, bears, or what-have-you, have pressure-plate drowning traps, have FBs or dragons hidden behind enticing artifact doors, make narrow Durin's bridges to nowhere with very infrequently activated spikes (so that an adventurer will walk out onto the bridge, look around, say "huh, nothing here," and then start back only to suddenly have the spikes activate and make him dodge off into the darkness), have rooms that seal themselves the moment someone walks inside, have corridors with spikes at random intervals activating in different sequences, have corridors with crushing or dropping bridges activating at different times, have a large arena ringed with coffins watched over by a necromancer and filled with dangerous undead beasts, whose count grows with each foolish adventurer, and so on and of course a magma chamber, and bridges over magma, and so on. The more dwarves die, the more excuses you have for more traps. Hell, you could have a room which kills people with smoke inhalation. The only condition is that it keeps expanding as more dwarves die and as it keeps expanding you keep adding and activating more traps to seal off the filled sections so that you can never again access them without dwarves dying in huge numbers (which would prompt more expansion of the crypt). I'm thinking of a Dark Souls/early roguelike style endless dungeon/catacombs vibe with infinite amounts of ridiculously dangerous traps which ARE POSSIBLE TO GET THROUGH WITHOUT BREAKING THE WHOLE THING DOWN but just require insane amounts of luck and many attempts to ascertain how they work.