For me, it's Shadow of the Colossus. I've been playing the game for 20 years and its atmosphere and desolate world are still unmatched. I've put countless hours into exploring the map even though there's little to find beside lizards, fruit, and the odd landmark. It's got a real sense of mystery, history, and rumination that continues to captivate me. When it comes to adventures, the less explained the better.