wanted four 1*1 vertical shafts that descended from a mountain crag all the way down near the bottom of the map into a huge common room. and this map had huge cliffs and a million z levels. was thinking mainly how having an outside tile present seems to allow you to see a long way in adventure mode when you are near it, giving an imitation of lighting. and having lit tiles in a main dining room to hamper cave adaptation. and there were wall grates at intermediate areas and drainage in the bottom to save from accidental flooding caused by future projects like tower cap plantations and irrigated underground farms.
so, i made massively tall up down staircases, and then started designating them for channeling out, from the bottom up. thinking that the dwarfs would stand on one staircase and do the one directly underneath him, allowing one dwarf per shaft to go all the way up to the surface, at which point i would open the grate and let him out.
turns out when they have nowhere to stand they dig the floor underneath them. my 2 embark miners got severe injuries, and i thought it was from the very fearsome wildlife.
then the two peasants who migrated in and were presented with their forbears bloodstained picks and mining hats died. and the next 2. and then the next 2. and i was always busy somewhere else, not noticing how these damned dwarfs were dying. i only figured it out when i lost my 2 picks into the ungrated drainage channel at the bottom of one of the shafts. i had some metal but there was no wood to use it and i couldn't mine coal without picks.
due to unrelated craziness (read: bears, cougars, one lone giant eagle, two berserk camels and some giant desert scorpions) it took 2 years to finally get a damned pick from a caravan and some wood to make more. and in that time i got an angry mayor, dungeon master and captain of the guard all wanting rooms, and had my entire fort sleeping in a barracks in the depot. thank goodness i had some save irrigated underground farms going before i lost my ability to dig. alcohol, prepared meals and engraved everything saved the fort. once i got going again i found its very simple and easy to excavate shafts like mine from the top down. miners only fall 1 z level at a time that way, rather then 15.