The area can only be accessed in True Torment Mode (NG+) and was added as part of the Stir of Dawn DLC. It requires the Weight of Sin ability to be enter. Plunge attack the rocky ground in the section right after the first Prie Dieu altar in the Holy Line. In order to enter the stone temple, one must have Petrified Bell in their inventory.
Points of Interest
Found at the far right from the stone temple.