In the mid 1980s I was policing out of Slaithwaite. In a quiet moment on Sunday a colleague and I borrowed the key from the Marsden signalman and drove into the closed tunnels to explore.
With the help of a torch, I could see a number of symbols painted in white on the walls of The Cathedral including, in a high position, a pentagram.
Certainly someone had gone to quite some trouble to leave those occult symbols, although that in itself does not prove that the space was actually used for rituals.