Poros consists of two islands: Sphairia, the southern part, which is of volcanic origin, where today's city is located, and Kalaureia, 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 centre of the island. It has a good road network and adequate tourist infrastructure, which makes it a popular resort for short holidays, as it is easily accessible from Athens.