The easiest way to gain it is enter from the hidden path.
But they did well to change it, now your visits must include some time in it and why not some engage. Even in unnamed city it’s the same, before, only by touching ground you were unlocking the unnamed city, now you need to walk inside of it a bit.
Still we have a really bad function, there’s no good without evil, sometimes you have to visit some places lots of times until the location is visible on your map. And this is wrong, it needs fixing.