This sounds as somebody who wants to make a kind of RPG mechanics - especially open world - with the main difficulty on how to fill it, but this can be usefull for all type of games.
And this is a real question because even games AAA become mostly boring when they propose to the player over and over the same of design: Go to point A, kill some rats, get this item (the lost sword of my Grandpa), Go to point B.
Just this system over and over in an incredible more and more beautiful painted world.
So my answer would be, maybe kind of laborious, but invent a story, don't spare at