1. Hit the essentials + a few extras in one/two go(s): * Parthenon on the Acropolis (try to go early and avoid the large crowds) * Walk down through Plaka for coffee, baklava, ouzo, souvlaki * Then cross Ermou street for shopping from Syntagma square all the way to Monastiraki flea market * Catch the Evzones changing of the presidential guard at the Greek Parliament in Syntagma Square 2. Athens Riviera - Go for brunch in Glyfada downtown, Vouliagmeni downtown, Floisvos/Alimos areas - Walk by the ocean and enjoy some freddo cappuccino and freddo espresso - Spend an afternoon swimming in Glyfada and/or Vouliagmeni (either in organized or unorganized beaches) and enjoy the sunset - Visit Lake Vouliagmeni for a night drink - Visit the Temple of Poseidon in Sounio 3. Some other things to see... - Ancient Agora (Market) in Athens downtown close to Monastiraki flea - Lycabettus Hill - National Garden behind the Greek parliament (free, shaded, and nice for a mid-day walk)
All the Greek islands are awesome! So there is no right and wrong choice. If you only have 2-3 days to visit an island, you can visit one of the Kiklades islands. Specifically, any of the following are beautiful - Syros - Paros - Milos - Sifnos - Naxos - Santorini - Mykonos * For Ferry information, please check the Travel tab for more information and websites. ** You can rent a car in the islands, but drive carefully since the roads are narrower than Athens. There are buses too, but they can get crowded. There are some taxis too, but only a few.
For quick trips, Nafplio or Aigina island make perfect day trips from Athens! Also, Syros island is very close to Athens and you can spend a night or two there! It is a beautiful island to visit. *Note: For Nafplio, you will need to rent a car to get there.