Find the Page of Corporeality

Journal
''The Oracle tasked me with finding 8 pages of the Book of Dire Prophecy! One of the pages could be found somewhere here in Brittany. Although the ruins are in an area outside the protection of the Oracle, rumors exist of underground passages into the ruins of the old world that can bypass this.''
 * What you actually need to do, is enter Central Brittany and find a secret entrance in Brittany Castle, that has an Obsidian Chest inside it.