It will not be long until Christmas and for the markets to be set up and a certain spirit begins to appear in people. You will go to Greece in that month? Well, if you have decided to visit Greece in December and January you should know that you will find significant discounts, much less people, clean air in Athens and a lot of movement for the Christmas holidays, the new year and the Epiphany on January 6.
Holidays in Greece are a special time that begins on December 6 with the Feast of Saint Nikolaos, when the Greeks exchange gifts. If we compare the Greek celebrations of Christmas they are much more solemn than ours, at this point very partying. It is rather a moment of family reunion and hope, without so many commercial overtones.
The city of Athens usually organizes a event program from December to January 6, with a Christmas tree and markets. Keep in mind that many shops and museums close at this time so find out which ones and what days. It may be that the means of transport heading to other corners of the country will be full of people on the same date as well, so the advice is patience. You will have a great time, but be patient.