I just spent a few days in Thessaloniki.

Unfortunately, I can't comment on the Hyatt, as I didn't stay there. However, it is located way out of town. If there is no shuttle service to the city, you should be aware that a taxi to the city costs approx. € 20 oneway. You can also take the Bus No. 78 which operates every 30' - 45'. I am not really sure about it, but as far as I remember, it takes 45' - 60' to the city depending on the traffic situation.

Generally speaking, Thessaloniki is a very nice place to go for a few days, but you should keep in mind that there isn't that much to see (considering e.g. museums etc.) compared to other cities like e.g. Athens.

You might want to go the White Tower (closed on mondays, afaik free admission on sundays; there is a permanent exhibition on the history of Thessaloniki inside the White Tower): http://en.wikipedia.org/wiki/White_T...f_Thessaloniki. I'd also suggest to visit the Museum of Byzantine Culture: http://www.mbp.gr/html/en/index.htm. If you are interested in photography, please check out http://www.photobiennale.gr/ (the Museum of Photography is located in the harbour area, access via the entrance at the northern end of Leoforos Nikis St.). This Photobiennale event includes various other exhibitions at galleries in the city. For dinner or lunch, I would recommend the restaurants in Katouni St. (http://maps.google.de/maps?q=thessal...ed=0CBgQ8gEwAA).

As the Hyatt is situated very close to the airport, a daytrip to Athens could also be an option. There are some flights from Athens to Thessaloniki rather late in the evening, so you would'nt have to hurry.