Just to the east of nearby mainland Galatas is the Lemonodassos a unique hillside grove-forest of over 30,000 lemon and orange trees. Car rental from Poros is a good choice for such excursions.
Or rent a car in Athens–at most a 4 hour drive away. If you already have a vehicle you can drive to Galatas on the Peloponnese and leave your car on the mainland or ferry it across. Separated from the Greek mainland by 400 meters, it is only a 5 minute boat ride to Poros.
The name Poros itself actually means 'passage' and refers to the channel (canal photo right) between the island and the Peloponnese. Etymologically speaking it is probably related the source of the English words porous and pore.
Poros is actually two islands: Sephaeria (or Sferia) and Kalavria linked by a very small canal or isthmus. Kalavria, the larger island has the smaller population, sandy beaches and more greenery.
There, many cyprus, olive and pine trees offer shade. Sephaeria, the location of Poros Town, is actually a volcanic out-cropping and forms Poros' southern tip.
Little Sephaeria popped out of the ocean in a volcanic bubble during the eruptions at Methana on the mainland. Kalavria is a much older island.
Islanders usually bathe at Alyki or the coves of Askeli and Monastiri all of which are reachable by bus. Those with boats may find many secluded coves and unvisited beaches along the islands shores.
Poros Town is the main community center of the island and its main harbor. A blue clock-tower dominates the skyline and is the island's landmark. The town itself is built around the harbor basin and rises into the surrounding hills as is common on so many Greek islands. You can find marvelous vistas and good hiking by climbing the narrow streets toward the back of Poros Town.
Northwest of the causeway and Poros Town is the National Naval Academy. Sometimes you can see an old battleship at anchor there.
Many hotels have their own restaurants. The 3 Brothers Tavern and the 7 Brothers Tavern both offer authentic Greek cuisine at reasonable prices and of good quality.
Many taverns line the limani and all serve good food and have excellent views of the harbor and Peloponnese across the strait. Hoist a few at the hot spot Coconuts if you're looking for late night bar activity.