Can't find Siona priestess and talk to her - the priestesses are in a cave in Arcadia - the entrance to their cave is in the north / west of the Sorone
Assassin's Creed Odyssey Ancient Tablet Locations Map
Ainigmata Ostraka in Arcadia in Assassin's Creed Odyssey - Assassin's Creed Odyssey Guide | gamepressure.com