Symmetry Achievement in The Witness
Activate the Symmetry laser.
How to unlock Symmetry
The Symmetry laser is activated by first completing the symmetry puzzles in the Glass Factory area, and then the symmetry puzzles on Symmetry Island. The Glass Factory area is located between the Entry area where you first start the game, and Symmetry Island, which borders the Desert Ruins area. No knowledge of other puzzle types or areas is required to complete this area, making it one of the easier areas to complete.
For a walkthrough of the Symmetry area, use THIS LINK for all puzzle solutions. Note that there is a ring of puzzles around the outer rim of Symmetry Island that are not required to activate the laser.
Once you open both doors and get to the lasers, solve the symmetric puzzles, activating the laser, and the achievement will unlock.