Poros is a small island-pair in the southern part of the Saronic Gulf, at a distance about 58 km (31 nautical miles) south from Piraeus and separated from the Peloponnese by a 200-metre wide sea channel, with the town of Galates on the mainland across the strait. Its surface is about 31 square kilometres (12 square miles) and it has around 4,000 inhabitants. The town of Poros has most of these inhabitants. Like other ports in the Saronic, it is a popular weekend destination for Athenian travellers.
Poros consists of two islands: Sphairia, the southern part, which is of volcanic origin, where today’s city is located, and Kalaureia, also Calauria (meaning ‘gentle breeze’), the northern and largest part. A bridge connects the two islands over a narrow isthmus.
Poros is an island with rich vegetation. Much of the northern and far eastern/western sides of the island are bushy, whereas large areas of old pine forest are found in the south and center of the island. It has a good road network and adequate tourist infrastructure, which makes it a popular resort for short holidays. Though possessing no airport, it is easily accessible from Athens via ferry or hydrofoil or from the adjacent mainland at Galates.
Read about Poros Island’s history at wikipedia