For many, Thessaloniki is a happy alternative to the chaos of Athens. Although it's home to just under 400,000 people, it's the second largest city in Greece. There's a large student population here, and so you'll find the city busy with cafes, pubs, clubs, and restaurants.
Of noteworthy mention is the iconic White Tower, built in the Byzantine period and still standing guard over the waterfront. There are a number of other Byzantine monuments around as well, including the churches of Acheiropoietos and the Heptapyrgion castle.
The Old Town is worth exploring as well, which has a classically Macedonian feel to it.