Thessaloniki in October

April through June gives you perfect weather - warm days, cool evenings, and the city waking up from winter hibernation. May hits the sweet spot with 22°C temperatures and everything in bloom. September through November works just as well. October especially - the summer crowds have gone home, but the weather stays warm enough for evening walks along the waterfront. Plus you get harvest season in the nearby wine regions. Winter isn't terrible if you don't mind some rain and 10°C temperatures. The advantage? You'll have the museums and Byzantine churches mostly to yourself, and the tavernas get cozy with their wood-fired ovens going. Skip July and August unless you love 35°C heat and humidity. The locals who can afford it escape to the islands, leaving behind a city that feels half-empty but twice as hot.