Regardless you've already pass the room, I'll just share another option here.
Actually its not invisible if you know the trick, here's another way:
You can use battery (forgot the name but looks like blue neon) you found inside the academy rooms, one on the west room (storage) inside the academy, master corpse in library, and cabinet in library (make sure you have 3-4 batteries).
Place those batteries on the east side of the room with lightning logo, move the mirrors there to face north, go to northern room (which is library) move the mirror to face west, go to the middle road and move mirror to face north. Now you can see the barrier. After that place one battery on the side of the lever (if i'm not mistaken), move those batteries to 2 lightning logo, move the lever, voila! the barrier is lifted.
Last edited by scrapyard123; 20/09/17 04:22 AM.