Secret #8 - JernAndrews/Control-Archipelago GitHub Wiki

from the Quarry Entrance Control Point, go towards the Quarry and head through a tunnel on the left, following the tracks, reach a area with forklifts and stone blocks blocking a path, levitate through a gap or launch the forklifts to destroy the blocks, go inside and drop down to the area with the toxic mold below, which is the hidden location