[Ant Attack] Maps!
It's not the easiest way to create multi-level maps, but it sure is the fastest for anyone to get going with. You can, in fact, open up Paint Brush in Windows now, pick an image/map size, scribble some walls in, drop in a magenta pixel for the player start and then load it into the game. There 30 seconds you have a map!
Once you've gotten over the joy of running round a scribble you can go back and start refining the map. This is normally done by writing your name and then running round that! After that it's time to expand upwards, each .bmp file is given the name levelxxx.bmp where xxx is the height. Shown below is level1.bmp (scaled up!) of a 17 level map, the last file unsurprisingly called level17.bmp
Below is the full 17 level glory (well not full as you can't see the top, but you get the itea).
1024x768 71kb gif
I found that using PhotoShop and keeping each level in a layer worked well.
Levels can be any size, within CPU power I guess, as long as all the level images are the same dimension. So above we have a 32x16 size map, I've also played with 512x512x8 sized maps with no problem. For the record the original Antescher is 128x128x6.
Some people may say, "well wouldn't it have been easier to create a custom level editor". My answer is well, maybe, that's still possible, just as long as the editor outputs .bmp files. Consider the .bmp file the level file format and anything that can write .bmp files a level editor :)