Witch’s Basement, upon returning with Mimir’s Head as part of the main story. You’ll have create light bridges to connect to the Nornir chest. To the right of the Nornir Chest is an explosive crystal that’s accessible by creating a light bridge.
Pick the crystal up then throw it at the red sap covering the opening by the ledge. Once attached, ignite it with a shock arrow. Climb up the ledge to find one of Odin’s Hidden Chambers. The map is on the floor to the right, beside the coffin.
Before entering the Witch’s House, find the mound beside the turtle’s left front leg, beside a rock.