Lightning Returns: Final Fantasy XIII is aiming to have a more open-world structure to its level design.
There was some criticism towards Final Fantasy XIII due to its very linear level design. It lacked the large areas that were akin to the series ever since the first game came out. Final Fantasy XIII-2 somewhat addressed this problem, but it wasn’t really an open world game.
“Our games have never put too much consideration into the idea of ‘being able to go to areas that look accessible,’ so we’ve made it our goal to take that part a step higher, Covering 100% in those regards might be a little difficult, but I’d say that you’ll be able to go to about 90% of all visible areas.”
The world that Lightning will explore in Lightning Returns: Final Fantasy XIII is said to be seamless with minimal loading times. Hopefully the areas are large and is littered with life like in previous Final Fantasy games.