So I hoped to enter this months challenge. Working with a bunch of maps in the same style seemed an invitation to scripting so I dashed off write a gimp script to take a map template like this:
and running the script creates a map like this:
It works, but I'm still playing with the script and doubt I'll be able to make a token set for the map, unless I just crib from by clip art (which is what I would do for my self).
One thing to note is that the output has been cropped in by one grid on all sides, a step that was necessary to allow connecting tunnels and shading to work cleanly at the edges, but I'm still not happy about it...