Lagonissi (Greek: Λαγονήσι meaning "rabbit island") is a seaside residential area in the southern part of Kalyvia Thorikou in East Attica. It is situated close to the shore and on a peninsula by the Saronic Gulf. Lagonisi is located approximately 30 km southeast of Athens and 35 km northwest of Cape Sounio. Being filled with luxury homes, beaches as well as 5-star hotels, that lie within the vicinity, it is one of the most expensive areas in Attica Prefecture. Restaurant facilities, cafeterias and bars are located mainly at the heart of Lagonissi, close to Kalyvion Avenue (the road connecting Lagonissi with Kalyvia Thorikou). It is part of Athens metropolitan area.
Lagonisi has many beautiful sandy beaches including those of Pefko, Agios Nikolas and Galazia Akti.