Cape Sounio, located 68 kilometers south of Athens, is mainly known for the Temple of Poseidon, one of the major monuments of the Golden Age of Athens. The remains of the Temple stand on top of a cliff, 60 meters above the sea. It was constructed between 444 and 440 BC during the Golden Age of Athens with the political leadership of Pericles. The architect behind this construction is thought to be Ictinus, who built the Temple of Hephaestus in the Ancient agora in Athens. The site also contains scant remains of a propylaeum, a fortified tower, and, to the northeast, a 6th-century Temple of Athena. The total number of the slender Doric columns of the Temple of Poseidon were 36, of which 15 remain today. The marbles of the Temple were extracted from an ancient marble quarry which is located in the neighboring valley of Agrileza in Lavrio, approximately 4 km north of the Temple. The Temple of Poseidon was a sacred place for ancient Greeks and especially seafarers who offered gifts and made sacrifices in order to propitiate Poseidon, the God of the Sea. It's ideal to visit early in the morning or head there for sunset to admire the spectacular view.

Lake Vouliagmeni is located south of Athens and was created when part of the roof of a large underground cave collapsed about 2000 years ago due to erosion and tectonic movements, which is why there are no reports from antiquity, not even by the ancient author Pausanias, who described the Vouliagmeni peninsula. The lake is globally known for its labyrinthine underwater cave that has not been explored yet, but already stretches along 3,123 meters, with 14 tunnels and one of the tunnels has a length of 800 meters. The lake is known for its therapeutic properties due to the constant warm water temperature and the rich content of hydrogen sulfide. The lake hosts the only existing population of a species of sea anemone, Paranemonia vouliagmeniensis, and it has been declared as nature protection area of Natura 2000.