Pagedslipped was my magnificent 40d city/megaproject. A 40+ level tall hollow glass pyramid, with all the living quarters, workshops, production halls, and other rooms housed in glass buildings attached to the inner surface. On the bottom-most floor of the pyramid was a great circular magma moat, with the many glass furnaces and other magma-powered industries atop it, and in the center was a deep water cistern fed by the underground river. Out of the front of the pyramid ran a 90 tile long retracting bridge trap which would fling entire sieges into deep kill pits flanking it, and conveyor belt assemblies made from arrays of retracting bridges at the bottoms of the pits would then convey the goblinite into safe collection areas under the pyramid.
Pagedslipped housed many experimental pieces of high-tech machinery. An automated breeding engine housed 12 pairs of wild rabbits, with a water logic computer counting them and sending any excess adults to a drop shaft with a refuse stockpile and butcher's shops at the bottom. This created an automatic supply of meat and bones for my dwarves. Shortly before I stopped working on the fortress I installed a second breeding engine using wild camels. Three automatic magma incinerators dealt with waste from the butchering operation, again without needing any micro-managing from me. As mentioned above, I built a large array of drawbridges to fling goblinite from the kill pits into a safe collection area under the fortress. I also made clever use of pressure plates to automatically separate children from the general population and divert them into a 'boarding school', an isolated sub-fortress where they would live until they reached adulthood and would then be automatically returned to the general population.
Here's an outside shot of the not quite finished fortress:
Here's a shot from inside, looking up at the roof: