I need some ideas and features for a megaproject in DF2010. Now, what I've been thinking of is a sort of plumbing system for both water and magma. I don't mean like an obsidian caster, either. I mean like a full fledged sewer system with control stations, grating over the water or magma, and snakelike tunnels everywhere. Beyond that, I don't know how best to incorporate this. Perhaps this will be more of an underground city than a mere fort. The entrance to the tunnels below would be a large, foreboding archway (at least 7-9 tiles wide) that slowly descends into the earth. It would be lightly guarded. At the bottom of this large ramp would be a branch towards a quarry, the city entrance, and some other stuff.
The entrance would be a grand wall of stone and iron, maybe 3 z levels tall. It would be 4 or 5 tiles wide, and topped with fortifications for dwarves. It would only reach about 2/3s to the roof. It would have a small pit outside it, maybe 4 wide, 2 deep, and acts as a drain for the wall's true purpose: magma. The inside of the wall would act as a small magma reservoir, and a lever would open several floodgates, washing away any frontal attackers, and being returned to the pit where it would rejoin the main magma channel.
Also, is it also possible to entirely disable caverns? Or how about just pushing them down a few dozen z-levels?
Anyways, do you guys have anything neat to contribute that might work in a fort like this?