I've just finished a few minor construction projects.
First off: defense. The fortress is nestled in the upper right corner of the map. In order to keep watch over the rest of the map, I built two watchtowers in the west and southeastern sides of the map. Any invaders will have very little space on the map where they won't come under fire from my marksdwarves, and they cannot enter the gates without coming under fire from 3 directions. In addition, I made the fortress airtight by putting roofs over these watchtowers as well as the main keep of the fortress. I'm proud to say that only one dwarf child died when I collapsed the scaffolding needed to seal the roof entirely.
Second: sacrificial magma pit. I know this is probably standard fare for most of you here, but I rarely use magma for anything other than metalworking, so this is new for me. I punched a large hole into the magma sea, then I set up a chamber to throw prisoners into the magma. The pit is surrounded by a golden platform, silver statues, and engravings.
Finally: covered pasture, partially underground. I throw the rabbits out in front of the gates, since they act as a lure for invaders and they replace their numbers easily, but my other livestock animals were getting crammed in pretty close in my walls. The donkeys were especially testy, and they were beating the shit out of eachother pretty bad. So I carved a nice little enclosed pasture into some clay. Subterranean plants are growing in the clay, so my livestock should have plenty of space now.
All I need now are some invaders. It's been forever since the last siege, and I'm getting bored.