First let's start with when it's not the best time to go. Late June and July are the hottest months in Greece, and all the concrete that is Athens tends to retain and amplify both heat and humidity. Combined with the smog from all the traffic they can make your days in Athens kind of "sticky".
August is equally hot and humid, but the city is practically empty. The vast majority of Athenians take their month-long holiday in August - most go back to their ancestral villages - so Athens becomes a ghost town and a very comfortable place to move about. Between June and August rainy days are very rare in Athens.
If Athens is just a short stop on your way to another destination or island, don't sweat it. Your time in Athens will be memorable at any season. If you find yourself there in the middle of the summer heat, avoid being outdoors between 11 AM and 7 PM. Either plan to be in the cool rooms of a museum, or do as all Athenians do and retreat to your room for a long afternoon nap.
All the stores close between 1 and 6 PM (not the museums and tourist shops), and the city comes alive after the sun has gone down, around 9 PM. It stays that way until the wee hours of the morning since there is no "closing time" for bars and night clubs.
If you plan to spend a week or more in Athens, and you have the luxury of picking the best time, April and May would be best in terms of weather and prices.
April and May are beautiful in Greece. You will still get the occasional rain showers, but most of the time the sun is shining, and the temperatures remain comfortable day and night. September and October are also a good time to visit in terms of temperature, but rain showers can be persistent after mid-September so plan and pack accordingly.
Between November and late February you can expect bitterly cold weather. Most who have visited Greece only in the summer have a hard time understanding how cold Greece can get in the winter. But such is the beauty of the Mediterranean climate that you get to experience each season in its distinct beauty: very hot summers, very cold winters, amazingly pleasant springs, and wet fall seasons.
Don't expect to see much snow around Athens in any seasons, but do plan for the temperatures to hover a few degrees above freezing most of the winter days. Even through the cold days the sun is usually shining in the sky so you won't get the depressing gray cloud cover customary in north America and Europe.
Athens is the main hub of all who travel to and from Greece. Chances are you will pass through Athens on your way to other Greek destinations, unless you fly directly to your destination via charter. The vast majority of visitors to Greece fly to and from the Eleftherios Venizelos international airport, and if you head for the islands, you will use the two major ports around the city, Pireas and Rafina. Those whose final destinations are on the mainland, will most likely pass through the Athens bus and train stations.
Click here for more information and details about getting to and out of Athens...
Traffic in Athens is notoriously inefficient and congested so driving in Athens is not recommended, especially since there are better alternatives. You can get around comfortably by Metro, by bus, or by tram. You can use the integrated ticket (1.50 Euro in 2012) for multiple rides in any of these transports for up to 90 minutes after it is canceled. You must cancel your ticket as soon as you enter the first mode of transportation and keep it with you at all times. After 90 minutes of travel, you need to cancel another ticket.
By far, the best way to get around Athens is by Metro (or Attiko Metro, or subway, or tube). It is safe, clean, punctual and connects all major areas of Athens with subterranean and open air trains. The Attiko Metro connects the center of Athens to the suburbs, and to other transportation hubs like the airport, the train station, and the port of Pireas.
Each Metro station is adorned with the art of contemporary Greek artists, and in certain cases the subterranean station walls offer glimpses of ancient artifacts. For example, the Monastiraki station has an open area where one can see the ancient sewer pipes and the Syntagma station has on display a host of ancient artifacts, unearthed during the construction of the Metro, and a wall representing a subterranean cross-section with embedded artifacts and graves. The Acropolis station sports copies of the Parthenon sculptures.
See and print the Athens metro map ...
The entire city of Athens is also served by a labyrinthine network of buses, trains, trams, metro, and trolleys. To find a route or a bus number, visit the Athens Urban Transportation Organization. but be prepared for long searches.
Last, you should never attempt to rent and ride a mopped in the streets of Athens unless you like living dangerously.
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