This is similar to what I remember from playing Operation Flashpoint: Cold War Crisis. I wasn't very good at the actual game, but there was a post-credit sequence I would skip to where you could just walk, drive, and fly around quiet, rural, and sparsely islands. The simulation is pretty unremarkable by todays standards but being able to explore a huge open world at my own pace was incredible at the time.
One encounter that stands out in my memory was of driving along a remote road in the middle of the night and coming across a bad traffic collision where a truck had completely crushed a small car along with its driver. Something about the brutal and almost mundane nature of the encounter has stuck with me.
For you and the GP I would recommend picking up Horizon Zero Dawn. The environments are gorgeous and vast, with lots of "story" in the placing of props and such. The actual story of that game was prettt darn good too, but if all you want to do is roam around a beautiful landscape – and occasionally come upon murderous robots, but they can typically be avoided rather easily – it will certainly hit the spot.
One encounter that stands out in my memory was of driving along a remote road in the middle of the night and coming across a bad traffic collision where a truck had completely crushed a small car along with its driver. Something about the brutal and almost mundane nature of the encounter has stuck with me.