We spent 2 weeks in Greece which is the minimum I would recommend. I would recommend staying in Plaka while in Athens. There are many restaurants and shops in this area. Plus is it close to Acropolis and other archeological sites. We took several day trips from Athens, including Cape Sounion, Meteora and Delphi. It takes about 90 minutes to drive to Cape Sounion. I would go at sunset so you can watch the sun go down over the water behind the Temple of Poseidon. There is restaurant where you can have dinner right next to the temple. Meteroa, which means "suspended in the air" is a 4 hour train ride from Athens. It may be worth it to pay a little extra for a first class train ticket because it's quite warm and crowded on the train, but there are beautiful views of the countryside along the way. Women need to wear a long dress and bring a shawl in order to get in to the monasteries. Men have to cover their shoulders and legs too.
Delphi was my favorite day trip. We stopped in the picturesque town of Arachova for coffee and pastries on the way there. After touring the museum and archeological site, we had a late lunch at To Patriko Mas. We sat on the terrace under a mulberry tree that overlooks the Corinthian gulf. The food was great and very reasonably priced.
We took a short flight from Athens to Satorini. We paid ahead of time to check our bags because we knew our carryon suitcases were too big. This is only a 45 minute flight. It would have taken 5 to 9 hours by ferry and the ferry was not much cheaper. We stayed here for 3 days, which was plenty. Make sure you pack light because there are about 250 steps in Oia. The marble pavement is very slippery and the stairs are slanted. It is very crowded in Oia so I recommend booking a private tour to see other sights on the island, such as the archeological site of Akrotiri, Pyros, and the windmills of Emporio. Do not drink the water on the island because it is desalinated ocean water.
We took a ferry to Crete. It took less than 2 hours to get to Heraklion. We rented a car at the port and drove 2 hours to Chania. While staying in Chania, we went to Balos Beach which has the clearest turquoise. There is a ferry that deports from Kissamos and stops at Gramvousa on the way there. You can hike to the fort at the top of Gramvousa and see Balos Beach in the distance. There is a shallow sandy lagoon to wade in and deeper waters, but you will need to walk over some underwater rocks. The water was surprisingly cool for mid July, but felt refreshing since the air temperature was close to 100 degrees. There is no shade at this beach so make sure to bring sunscreen!
On our way back to Heraklion, we stopped at Matala Beach. This beach is surrounded by rock walls with caves you can explore for a small fee. You can also cliff jump if you are feeling adventurous. The entire beach is covered with small round pebbles that get extremely hot in the sun so make sure to wear shoes that can get wet!
