This chapter of Assassin's Creed: Odyssey walkthrough includes descriptions of all Ainigmata Ostraka hidden across Attika. Below, you can find helpful information on locating the following Ostraka: Backstage Pass, Killer View, Elbow Greece, Goat's Gruff, and War Eagle.
Location of Ainigmata Ostraka: Loom inside the warehouse.
Riddle solution: You will find the mask on the pile of blankets at the theatre.
Location of Ainigmata Ostraka: Mt. Pentelikos Marble Quarry
Riddle solution: Areopagus - city center. Approach the sacrificial altar and solve the riddle.
Location of Ainigmata Ostraka: The altar of love.
Riddle solution: There is a long walk ahead of you - see the map above. You need to reach the camp at Oropos Heights.
Location of Ainigmata Ostraka: Camp Dekalia.
Riddle solution: Cave of Pan - the bloody goat statue in front of the cave.
Location of Ainigmata Ostraka: Isle of Salamis - Salamis Marble Quarry.
Riddle solution: See the map above - it shows the location where you find the eagle statue and to the solution of this riddle.