Well if I have this correct Other than Midgar there is Kalm, Chocobo Farm, Fort Condor, and Junon left. I'm doubting it's at the Chocobo farm. The hint "the answer/picture has nothing to do with the plotline" makes me want to say it's in Fort Condor because that place is optional, but I don't recall anything that would fit the riddle there. Which leads me to believe it's in one of the houses at Kalm, and that's all I've got so far....