The weather in Athens couldn't be more perfect than it is in May. Similarly to April, it offers a "best of both worlds" vibe. The atmosphere is warm enough to feel like summertime (with average daytime temperatures hovering around 77°F (25°C)) but it's not stifling hot yet.
It's unlikely to rain (there are only four rainy days on average all month) and the skies tend to be sunny and bright. Just keep in mind that the evening temperatures do drop—the lows average roughly 60°F (15°C)—which can feel nippy if you're strolling through the markets or dining al fresco. For that reason, be sure to bring a jacket.
Another thing to consider is that, even though plenty of folks start hitting the beaches in May, the temperature of the water remains chilly so it's not always the best time for swimming. Additionally, the North Winds (the Meltemi) begin picking up over the Aegean Sea which occasionally impacts ferry schedules or make it unsafe to swim.
For more on weather this month, see Greece in May: Travel Tips, Weather, and More.
Crowds and Costs
The mix of pleasant weather with reduced crowds doesn't get any better than it does in May. It's the very tail end of the shoulder season which means the weather is at its best but the tourists haven't arrived yet en masse. To be sure, you'll see plenty of people—it's by no means low season.
However, the sizes of the crowds are considerably smaller at the major tourist attractions than in June, July, and August. Not only that, you can catch the last of the shoulder-season deals on airfare and lodging. Some hotels will have already shifted to high-season prices but if you do some research there are still bargains to be found.
Where to Go
The beauty of visiting Athens in May is that you can go practically anywhere in the city and have a great time. There's virtually no discrepancy weather-wise between one neighborhood and the next, and everything is open for business. If history and culture are of interest, check out the city's many museums or walk through its ancient archaeological ruins. If you're into food and dining, stroll through the laiki markets or check out some of the hip new restaurants.
You don't have to stay in Athens proper when you're planning your itinerary. There are lots of day trips available to destinations outside of the city that will still get you back to the city by evening. If you like learning about early Greek civilization, the Delphi ruins sit about two hours northwest of the city. There, you'll find the famous Sanctuary of Apollo (also called the Oracle of Apollo) which Greeks once called the center of the earth. Another option is to check out the wine region outside town called Attica—a famous cluster of vineyards that span 16,000 to 20,000+ acres and include upwards of two dozen wineries.
Another option is to take a weekend trip to one of the islands. Although some resorts may still be closed—especially earlier in the month—by mid-May most begin opening up to visitors. Check out Santorini, Paros, or Naxos, all of which have hiking and other inland activities if the water is too cold for beach-going. Plus, the ferries to these islands operate year-round.
What to Do
One of the first stops you should make when visiting Athens in May should be at the ancient Acropolis. The famous citadel, which was once the center of Greek civilization, boasts dozens of fascinating archaeological structures that shed light on how the people lived and governed. Don't miss well-known features such as the Parthenon, Hadrian's Library, or the Temple of Athena Nike. There will definitely be crowds this time of year but they won't be as bad as they get later in the summer.
If you head out of town, try exploring the Sanctuary of Apollo at the Delphi ruins where the ancient Greeks honored the god and consulted the oracle (known as Pythia). Over in the wine region of Attica, check out the acclaimed retsina wine at Papagiannakos Winery or the Strofilia Estate.
On the islands, try taking a hike or exploring the shops in town. In Santorini, you can visit the Ancient Akrotiri ruins (once buried in volcanic ash) or trek from Fira to Oia. By the middle of the month, many of the resorts will begin opening and the beaches will get warm enough to swim and lounge.
Events in May
Protomagia (May 1): On May 1st the Greeks celebrate International Labor Day which they call "Protomagia." Most schools and offices are closed and, due to the sunny season, many families use it as a time to go on picnics, pick flowers, and spend time outside.
Traveling to Athens in May? Check out these great itineraries.
Discover Athens, Mykonos, Santorini, and Crete - 14 Days. Immerse yourself in Greek mythology in Athens and Delphi before beginning your island-hopping adventure. Explore Mykonos and the volcanic island of Santorini, with a stop at the sacred island of Delos. Then head to Crete for hiking, history, and visits to traditional villages.
History and Culture in Athens and Santorini - 7 days. This versatile itinerary includes five days in Athens, along with two bonus days of the sunny island of Santorini. The latter portion of the trip will bring you to see the Ancient Akrotiri ruins, along with a wine tasting after visiting Megalochori and Pyrgos.