We've done several explicitly ASB/Fantasy/Sci-fi challenges in the past, so more suggestions of that sort are welcome!
Perhaps something ala
It came from Space!
Make a map in a setting where there's an invasion or expansion of something non-human (ala the Fae, The Thing, zombies, evil alien skeleton castles). It can have non fantastical things (invasive species or the Spread of Beatlemania) but the focus should be on scifi/fantasy.