The Talos Principle

In the World C hub area, there is an axe on the wall near the entrance to level C7. Take the axe and use it and the nearby boarded up doorway to unlock this achievement.

There are two axes in the game.

1) A: 10 star level.
You pick up the axe in front of: "Dumb Dumb Mine" (left puzzle upon entry) to chop down the wooden door / panel in the middle of the level (outside the puzzles). Then fly with the axe to chop down some trees in "Dumb Dumb Mine" to be able to solve the puzzle.

2) C: near C7 entrance
You will need the axe to gain access to all the Messenger levels. There is one in each letter hub.
However you will also need to bring the axe to free a blue emitter to get the star of the Hub world (behind the tower). This emitter can only be accessed through the ground floor of the tower. Note that freeing all panels at once before getting all red sigils is not recommended as the tower panel will void your achievement:

This achievement can also be popped by using the CRObar to break into the box room in world B7.

These can both be found hidden amongst the rocky outcrops surrounding the play areas of this world. However, be careful whilst searching around out there, because if you attempt to go too far in any direction then Elohim will forcibly reset you (he warns you with a chant whenever you approach a boundary; so don't ignore this and be sure to back away).

You might wish to be wary of finding and entering the box room for the reason given within the spoiler tag.