The Cathedral of Knowledge

The Cathedral of Knowledge is a planar realm which connects to The Nine Great Libraries. It also has a physical location, beneath the Notre Dame Cathedral in Paris, France. There is one door leading into the main chamber of the cathedral and eight doors leading out. The Master Index, a dusty tome of immense size, lies on a stone pedestal in the center of the chamber. It is by this artifact that one can enter the other Libraries. But perhaps an offering to satiate the mind of Master Index is necessary?