Trying to unlock it now, but I'm having trouble. Found the info you were talking about but it feels too vague on how to unlock it. The description is good to have as background details. But with it being the only detail to, I ended up getting lost and circling each of the areas trying to find a hidden detail that'd lead me to the mystery island.
Thanks for the hint. though it feels like something similar should be in the game. maybe a line of text saying "something similar seems to be on the guild map" in addition to the already existing text (although maybe you'd have to reword if you want to include both). just my 2 cents though. and again, thanks for the hint