I realize this is a very old thread, but I have a soft spot for the old school blue D&D maps, and I'm a newbie here.

I've gone through this with gimp 2.8.22 on linux, and it works great - thanks torstan!

A question, though - it's been so long, I'm having a hard time finding a set of map elements to use. I can draw my own, of course, but there has to be a still-extant set available somewhere?