Thank you, I found it, though it wasn't marked on the map, I had to "poke" the wall in the spot you showed on the picture, just like with the Succubus tower, first time, and then it appeared. I wouldn't have guessed it's there if I wasn't told. Maybe my perception stat is low or something, I don't know, but thank you nonetheless.
I also found the slavers's hide out, and it has a dev lock, saying it will be implemented in a later version. I guess that's where it ends, for this update at least?