I've lately taken to carving out castle-type fortresses from the summits of stone hills, and building 3-wide tunnels to other sites on the map that I want to exploit.
The main burrow of my most recent fort is about three z-levels deep, and my food production burrow (beneath a grassy valley, about three localmap tiles to the west) is another z-level. The only route into the main fort is a sloping 3-wide tunnel about 5 z-levels deep between them (which doubles as a secure caravan route and Tunnel Of Goblin Death from the western border - there's an early warning system at the other end). I've also fortified the top of the main burrow with a curtain wall another z-level high - it will be at least three when complete - and have my primary mine shaft under a microcline pagoda whose roof stretches three z-levels up. A six-z-level-high smokestack comes out of my underground refuse stockpile too, to leach miasma into the atmosphere without smothering my dwarves.
The farms are so far away that the place is inefficient as hell, but it's really cool-looking. A cross section of the whole thing looks like this:
CROSS-SECTION: Smokestack
Not to scale. # ##
# ||#
|| Outhouse Jail
Pagoda || | |
| || V V ....
___ /_\ || ____ ___ |
Depot | |_|>|___||___|__|_| | | <- Workshops, Outdoor Stockpiles
_____ |___|X|_______________|_ | <- Vault, Main Living Area
.........| _ |..| __|X|__________| |_|
| ___/ __/ \____/ |X|__|
...|__/ __/ |X| Main Shaft
../ / ___/ To entry and farms
That little outcropping on the edge is actually the extruding part of my jail cells. Each one has a bed and a restraint behind a locked door. Since I ran out of cliff while building them, each one extrudes one tile over what will be a moat once I find a better water supply. In addition to using them for justice, It lets me lock any dwarf I want in by drafting or assigning them the bed, and gives them a convenient place to drown themselves if they go nuts.
And yes, that is an outhouse. Its a little building built over a small water tank. (which until I build an aqeuduct for running water, gets hand-filled by a bucket brigade) A lever in the building flushes the contents of the water tank into my refuse stockpile. Since dwarves don't actually need latrines, I use it as a garbage dump.
The best part is that about four pages of corpses tells me that there's a chasm and cave river on this map, in addition to the volcano on the eastern mountains. Running water + magma + safe drainage + a few years = epic fortress.