Opposite the shore of Lake Keri, Marathonisi (the island of Marathias) dominates, which adorns the bay of Laganas and its shape resembles a turtle. The island, which has two poles, the Pontic Islands, was once connected to the cape of Marathias. It has about a mile perimeter. The nature there is exotic, the sand is crystal clear and the waters are clear. Apart from the two beaches, one with pebbles and one with sand, one can also find rich vegetation, olive trees, green oaks and pines, a lot of fennel grows from where the name of the island comes from. In the northwest of the island, high cliffs rise. Caretta-Caretta turtles make their nests on the blonde sandy beach that stretches like a language in the sea. Guardians of the National Marine Park, they live there permanently and protect the island, the turtle and its eggs. On the steep shore with pebbles there are two small sea caves in which one can enter with a small boat. You can visit Marathonisi by renting a boat from the beach of Keri or Laganas, or asking Kaikia in Keri to pass you. The island is pristine, there are no shops, so remember to get water and food if you plan to stay there long enough.