To get this achievement, you must read all six notes in the same playthrough, in Normal mode. (Not Noir mode, which is a mode you unlock after playing through the game the first time.)
1. Once you start, there's a note in the room with you, on a piece of furniture near the wall above the staircase. (You walk beneath it when you go downstairs.) Go downstairs, get your coat on, and go outside.
Follow the road throughout the entirety of the game, and you'll see several visions of a woman that'll disappear once you approach her. She'll be saying something backwards repeatedly while you're near her. She'll always be standing on a note that you must read to get this achievement.
2. The first time you see her is just down from the cottage you start in. Impossible to miss.
3. Second is after you've gone down a ways, past a deer, and started making your way up a hill again. She'll be on a tall rock on the left hand side. You need to go past the rock and find a red boulder. Push it down(physics based), then jump from the nearby small rock onto the boulder, then from the boulder onto the large rock she's on.
Note that the red boulder can be a bit finicky to position just right. Just keep trying, and you should be able to get up.
4. You'll see her immediately after going through a cave. It's the only cave in the game, and it's part of the path you're following.
5. Quite a while after the cave, after using a lever to activate a bridge that lets you cross a river, and even then a good amount of walking, you'll finally see her again on top of another tall rock to the right side of the road. There are other rocks surrounding it. Just jump on the three smaller rocks in a line between you and her to get to her.
6. You'll find her at the end of the road, standing near a lake and a tiny hut like structure that almost looks like an outhouse.
Once you've read the final note, the achievement will pop.