Let's talk about one particular theory of open world design. Basically, I think this approach is underused and very promising.
Fundamentally, it's like this: create hubs of a certain kind of play with outlying points of interest. Make sure the player can see those outlying points of interest from around a minute out, so that they naturally gravitate towards them if they are interested in that kind of play.
Arrange your map so that no POI is visible from another POI, and use travel along the roads to reveal other POI and minor play elements of the sort the player is expecting given the type of play attached to the POI at the end of the road.