From the Trapdoor Key platform, return to the closest rolling wheels-of-death corridor. Dash in and hook around the right corner when the time is right - you're in search of a niche in the far wall. When the time is right, dash to another niche opposite. One more to go. Stop the moment you enter the third niche - sliding razor doors are waiting. Evade a second razor door trap and the last secret is yours. You know the way out.