Here's my entry: Uveluben - Bearsoap
Ten dwarves, eight years, and 157 bears have created twenty level tall tower of dead animals and burnt trees set in an open cast mine. I like to think the elves die a little inside whenever they visit me.
The idea for this came when I was looking through the raws to find what animals would be the best choice to farm for this project, and while hippos and elephants give 10 fat their offspring take 5 and 10 years respectively to mature, whereas polar bears give 9 fat and take just one year to mature, making them my preferred choice. I modded them to be wagon haulers so I could buy some on embark (the only modding I did for this challenge other than setting different names for male bears), picked a nice flat tiaga forest with sand and sent in my dwarves "The Clean Beards".
I figured that dwarfpower wouldn't be much of a bottleneck so in order to maximise my fps I decided to only use ten dwarves, the minimum to prevent immigration. I got 22 volunteers for the last three spots in my second summer, but 19 fatal accidents later we had our full roster. Goblins didn't survive worldgen which makes life easier for a small fortress. The first few years were pretty uneventful as we waited for numbers to build, slaughtering the odd surplus male, after four years the elves offered me three grizzlies which I decided to buy, their numbers only really filled out as I finished. In later years I noticed that everything happens at once, I had eleven out of twelve female polar bears give birth in no more than 30 seconds at one point (luckily the grizzlies were on a different cycle); but we persevered and finished up my tribute to the beast that made it all possible.
My inspirationMore images in the spoiler.