Five save crystals along the St. Francis Folly level.
After saving progress, played put the keys listed in the lower part of the room, but before access could collect more items in a hidden room. However, in order to access it, a number of things had to be done in order to open the secret gate for a short period of time.
There was an unconventional switch, located somewhere in the huge room.
Where was the switch that unlocked the door?