While I have done a few dark maps in the past, I have yet to do a map with such a dark theme! I had this idea a while ago and I really wanted to make a very typical kind of cultist gathering place on the beach. These locations are common in games of Call of Cthulhu, the eldritch horror RPG that pits players against the unknowable machinations of the Old Ones and Elder Gods.
I may do some more of these in the future as you could use this kind of map in a D&D game to add some horror elements!
Oh there is also a night version with some creepy candles :D