Olsztyn is at its best in summer, when the surrounding lakes are warm enough to swim, the cafe terraces fill, and the Masurian lake region across the road is in full swing. June through August is the natural season; expect highs of around 22°C and long northern evenings.
Autumn brings dramatic colour to the forests around the city; spring is muddy. Winters are cold — well below freezing for weeks at a time — but the lakes freeze and locals come out for ice fishing and skating. The biggest annual event is the Olsztyn Summer Concert series in the castle courtyard in July.