This is a missable achievement from chapter 5. The game does have chapter select so you can return here if you miss it.
Note minor spoilersIn this chapter you need to place a nut and follow a squirrel after it grabs it. The paths can get convoluted. When you get to the third squirrel, part of its path (near the end) will go through some zig-zag logs and bramble, through a more open area on a downslope with a rock wall on one side, then down across a rocky cliff.
If you are following the squirrel directly (which isn't easy), in the open downslope area between the bramble and the rocky cliff, on the rock wall on the right hand side is an old animal blind/cabin. If you go into it you'll find a cassette tape from Nina and an old guitar. Pick up the guitar to unlock the achievement.
Note, that you can get to this building without directly following the squirrel (e.g., circling around a large boulder/rock from the side) and technically don't have to wait until you are on the third squirrel to get the achievement. Once you have free movement at the very start of the chapter you could simply go find the spot; it's just hard to describe where it is without following the squirrel if you don't know the area.