Spring and autumn are the best seasons for Kastoria. In May and June the mountains are still green, temperatures are comfortable for walking (15–22°C), and the lake is at its most photogenic with morning mist rising from the water. September and October offer similar conditions plus the turning of the leaves on the wooded slopes around the lake.
Summer (July–August) is warm and busy, with Greek tourists coming for the lake and the mountain air — noticeably cooler than the coast. It is still pleasant, just more crowded. Winter is cold (near zero or below) and sees little tourism; most things remain open, and the lake occasionally freezes, which is worth seeing if you happen to be here.
The Kastoria Fur Fair takes place in May and is a significant trade event rather than a tourist attraction, but it does animate the city in an interesting way.