890B (HP)

from section 6, walk through the newly opened door into the cube, then left into the next room to the cube, then left to the cube at the desk. Go back right (you need to walk into the cubes to open the door here) then go back downstairs to the atrium and search the same 4 cubes to eventually find the lens, but its broken. go back upstairs and right to the calculus room, then back downstairs to the power room to the cube, then back upstairs to the top left to luna's room, then back downstairs to the atrium and search the only cube in bottom left (achievement here)

Section 1: 0:45
Section 2: 0:55
Section 3: 1:45
Section 4: 3:05
Section 5: 7:20
Section 6: 14:50
Section 7: 17:05
Section 8: 22:40
Section 9: 22:55
Section 10: 26:30

Achievement Walkthrough: