Kokkinokastro ( Alonissos ) is located 7 km north east of Patitiri. It is white stone and pebbled with clear deep blue waters situated under a red rock cliff. Nearby, you will see some wall remains of the ancient city, the celebrated Ikos. Opposite the beach, on the islet called Kokkinonisi (Red Island) tools from the Palaeolithic area were found. They are the earliest evidence of human life in the Aegean.