Manifold Garden

After completing the puzzles that activate the yellow, green, and red lasers, you'll be able to pick up a blue cube on the platform that all three lasers shoot at. When you pick up this cube, you'll earn the "Let There Be Darkness" achievement.



You can unlock this achievement almost immediately after earning that one by placing the cube in its rightful home, which is located in the area that is flashing/pulsing. The world will return to normal and the achievement will pop.