A Lesson in Cartography in Potato Land (2012)
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It's definitely a game that rewards exploration, not just with finding random chests or gathering dumb resources for crafting etc, but exactly as the post hopes - because it's beautiful and atmospheric. I found myself spending a lot of time hunting in the game, not because I needed to, but just because it was nice to be out in nature. The game is 5 years old but (perhaps with the exception of RDR2) I don't think a single RPG since has got so much right in one game.
It doesn't capture exactly the sense of "being out in nature", but the exploration part ("omg there is another thing here?") is definitely there and it's nailed.