Thinking man's walking simulators

Games that emphasize aesthetically pleasing or otherwise interesting 3D environments to explore, but that also require some amount of thinking and puzzle solving, rather than just pure exploration / sight seeing. Mazes, object based puzzles, logic games all count, but the emphasis is on tranquil and at your own pace gaming, rather than agility based tests like platforming or fighting. A game like Portal, while super interesting, has too much focus on reflexes and puzzles, and not enough on environment and exploration. A game like the Witness, which is super interesting to explore, but also features very good puzzles is a good example of the kind of game we feature here, though games that are much easier to solve like "the Stanley parable" are also exactly the kind of game we like.