Oh I'd totally forgot about the Excutiata, I've added it to the Q&A thread.
I read it before I'd reached Golgotterath in the book and was waiting for it to be reffered.
So it's a ceiling fresco, literally an upside down painting of hell. A literal Inverse Fire in the most holy place of the Consult, and a matching one in one of the most holy human places.
The part that really gets me wondering is that it's based on pre-Arkfall Nonmen statues, long before the Ark or Inverse Fire came about...