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Search the chest near the western wall in one of the courtyards to find Berengar’s Notes. This begins the quest Berengar’s Blade.
Read the notes and then talk to Vesemir about them. He’ll tell you that Berengar tried to craft a sword but then lost the Diagram in a cave when he was attacked by a Chort.
Make your way to the cave marked out on your map. The best way to travel there is by following the river. Enter the cave and defeat the Chort. Search the cave for the Tor’haerne Diagram to complete the quest.