The best time of the year to visit Greece

If you start getting uncomfortable in the low 80's and wilt at 90 then by all means do not even consider June or July. The fall would be best, late fall at that. You'll have to trade less sunlight for temperatures you can tolerate.

September is too much like summer - I would pick October. It's a plus that you don't care about the beaches because you can spare yourself the summer time crowds - and you'll likely get good flight fares in October.

I was in Greece this year from April 22-May 6. Of course, my experience is anecdotal. The first few days were cool and pleasant, needing a jacket in the morning, happy to be in short sleeves in the afternoon. The second week, temps heated up to mid-high 80's. I was in contact with my tour guide afterward and noted that on July 1, the the forecast was for a high of 109F. She said it was so hot at Delphi that she thought she was going to faint.

Also check hotel prices. I had planned to stay in Athens after the tour - in May, but hotel prices jumped by about 30-40% on May 1, so I spent several days in Athens before the tour instead. Though hostel prices may not change much from month to month.

We go to Greece every October and find the weather mild, short sleeve shirts during the day, even most nights with an occasional light jacket during the evening. Some rain but never any washouts. The Aegean is still warm to swim in. Obviously there is no guarantee on what the weather will be like but if you go by the averages October is very nice and we can attest to that.

We just got back from 10 days in Chios, sunny, low-mid 70s, comfortable nights with one overnight of rain.

Best part of off-season travel is there are less tourists, lower prices and still nice weather.

As far as where to go there are many areas on the mainland and of course numerous islands. It all depends on your interests which appears to be more educational/history and enjoying beautiful landscapes. Too many areas of Greece to recommend so do your research. We're not beach goers but do love the coastline of the mainland and the islands. Spectacular in most places!

Check out the books: Blue Guide to the Aegean Islands & Greek Island Hopping. There are several travel forums to check out and one of my favorite websites is Matt's Greek Guide:
http://www.greecetravel.com/

I agree that October would be perfect timing. I also agree with Kaeleku that if it’s monuments and ruins you’re interested in, the western coast of Turkey has many worth seeing.

Assuming the visa situation is cleared up, you might consider combining Greece and a little taste of Turkey. You could spend your first week in the Peloponnese, then fly to the island of Samos and take a day trip to Ephesus in Turkey, one of the world’s finest archaeological sites.

You could return to Samos overnight, then ferry to Mykonos in order to visit the sacred island of Delos, then back to Athens for a few days.

Or from Ephesus you could bus up to Pergamon, which I feel is the most evocative site I’ve seen. The ruins of the temple on the deserted hilltop — and the perfectly preserved amphitheater (the world’s steepest) took my breath away. From Pergamon you could ferry to Lesvos and fly back to Athens.

I personally am not interested in seeing th controversial reconstruction of Knossos. I much prefer authentic sites. I encourage you to research Ephesus & Pergamon & see what you think.

I would go last two weeks in September. We went this year 9/18 to 10/7. The weather was perfect

Greece is an excellent choice to travel off-season. The weather is still warm and sunny, people are relaxed and hospitable, and the sea is calm. I'd suggest any date in June or September and even the beginning of October in order to avoid the crowds and still get the best out of what Greece has to offer. July is one of my favourite months to have my holidays in Greece but sometimes it gets too hot at that time, almost like mid-August. So, if you choose to make the trip in July, it better be before the 20th of that month.

I just returned from Athens on Tuesday. temps in 60s during day--sunny exc 1 partially rainy day--drizzle not a down pour. perfect temps, easy to still sit outside for meals. less crowds--better to see Acropolis this time of year---not wall to wall folks. I was also there in November, same temps.