I have one really good one. Sunken Atlantean ruin.
Channel out all but the border of an aquifer layer to make a giant lake, seal the outside of the aquifer using pumps and construction, then drain the lake. Remove the drainage system, then build a giant clear glass city in the deeps with dozens of domed subdivisions sectioned off, able to be individually drained and filled by lever-controlled self-powered pumps (They'd have to be started manually, but after that, they'd run till the lever's switched off. The blueprint makes sense in my head).
Bonus points for building the city around one or more central glass spires which go from the very bottom of the map to the very top. If its at all possible to find an aquifer and magma on the same map, bonus points for filling a core of the spire with lava for channeling to the forges and furnaces. If not, channel out a wide river leading off the map (and dammed to a height high enough to keep the lake full and low enough not to overflow its bed), then make the above-water portion of the spire a giant self-powered waterfall.
Build residential, commercial and industrial domes with easy access to each other, Sim-City style. Use z-level accessways between domes as well as horizontal. All individual homes, warehouses, offices and workshops should be built in separate stone buildings or apartment complexes. Any outdoor flooring may be made either of stone or colored glass. Each dome at least should be covered in a clear glass roof. Give the buildings as many gem windows as possible. Build a special room or plaza to showcase each artifact, and another to honor each legendary dwarf. Make as many rooms royal quality as possible, either through artifacts or lots of masterpiece stuff. If there was sufficient forward planning to use natural stone for the buildings, engrave them.
Fill the whole place with outdoor plazas, statuaries, menageries, fountains, amphitheaters, irrigated gardens and farms. Menageries would have bars and free-roaming animals, not just cages, and fountains would all work on a self-contained, self-powered water system.
If the map has underground water, add tree farms. If it has a chasm, add a lever in a hard-to-reach central control room that diverts the rest of the lake into a chasm, allowing the player to destroy his framerate and access the lakebed. If not, make one that opens a dam at the bottom of the lake bed and drains it off the map. If the map has Hidden Fun Stuff, build a special dome over it, seal it up, and build a glass temple to Armok above it with a lever-controlled trap near the altar so that sacrificial victims can be dropped within. Make another dome a City of the Dead and fill it with tombs for nobles and legendaries, plus a Great Hall of the Fallen featuring an alcove, statue, and casket for all remaining dwarves.
The only entrance to the final city should be through a series of natural stone tunnels beneath a small log cabin on shore. (Exception: there will have to be *some* construction where it punctures the aquifer) If possible, place lever-controlled adamantine double doors or floodgates to seal the entrance in an engraved subterranean gallery.
Remove the blockages to the remaining aquifer squares and let the whole thing flood over. For bonus points, build the cliffs around the lake even higher and pump water from the aquifer square to raise the water level of the lake. Flood all the domes one by one, killing all the dwarves except a legendary engraver as it progresses. Once he is the last dwarf alive, engrave the stone tunnels, producing masterpiece mementos to the glory of the city and its destruction by flood.
Then abandon the fort for adventurers to find and drool over. Extra points for modding in a race of amphibious sentients who could take the place over and challenge adventurers or reclaimers. Bullywugs, anyone?