The unused Cathedral key was supposedly to open the All Hallows level after Thames Wharf and Aldwych. The level was removed from the game before release and turned to a Bonus level. You need to have all Secrets 59/59 to play it after beating the game. So the Cathedral key is useless.
I know the one a PC version can adjust of course. And the PS1 version user uses of my video as a walkthrough guide. Therefore I played in the dark state.
