Conference Venue
Thessaloniki is the 2nd biggest city of Greece. It is the co-capital, and usually it is called the Bride of the Thermaic Gulf. It has many archeological sites and museums in and around the city and many more attractions close (an hour or two driving), like Chalkidiki (major touristic resort), Mount Athos monastery state and Olympos mountain.
To learn more about the city a good start is this link on wikipedia.