So I've started work on a new idea: A Puzzle Fortress! Basically, the concept is to build into the fortress a bunch of puzzles. Here are the ideas I've come up with so far:
Picross: A large room with a smoothed floor, with outlying single-tile channels filled with varying amounts of water/magma. These are the numbers you would find on the outer edge of a picross board. Engrave the tiles properly to cause the picture to emerge. A dual color variant could be created with the use of water AND magma, but I kind of suck at moving magma around. I imagine this will be easier with the addition of other fluids, such as acids, blood, milk, and so on. three dimensional variants, wherein the numbers coincide with spaces to be mined away, to create a sculpture are probably harder if not impossible to implement. the biggest issue with this is that you would never be able to have a row or column with only 1 engraved space, since evaporation is an issue. (If you glass over a cell with 1 water in it, does it still evaporate?)
Sudoku: I'm not fond of this game, but since it's easy to implement, I can give it a go. Simply a 9x9 room, with floor tiles of differing colors arranged in 3x3 chunks. The initial "numbers" on the grid are represented with visually distinct custom stockpiles. Beds, Statues, Booze, Gems, Doors, Tables, Chairs, Ammo, and Leather are used to represent the numbers 1-9. Since Sudoku isn't actually a math puzzle, this should prove to be sufficient. The player plays by designating new custom stockpiles.
Lights-out: I'm not sure if levers can be attached to more than one thing, or if things can be attatched to more than one lever. I'm sure it can be managed through pumps and pressure plates. Once you've got that though, you can build a system where the goal is to lower a bunch of drawbridges to create a path for traders or whatever. This is the only puzzle I've come up with with a practical application.
aaaaand I'm out of ideas. Honestly, the picross idea made me squee when I though of it. The basic idea is that we can use our dorfs to play puzzle games for each other: Yet another idea that DF simply wasn't designed for. Anyways, does anyone have anything to contribute?