Summer (June–August) is the prime season. The lakes reach swimming temperature by mid-June, the Villacher Alpenstrasse and Dobratsch trails are fully open, and the outdoor cafe culture of the old town is at its best. The Villacher Kirchtag folk festival in late July and early August is worth timing a visit around — it transforms the city centre for a full week and represents Carinthia at its most characterful. Accommodation is busiest and most expensive in July and August; book ahead for lakeside options.
Spring (April–May) and early autumn (September–October) are good for those who want comfortable temperatures without peak-season crowds. The Dobratsch nature reserve is at its most botanically interesting in May and June, and the lake cycling routes are pleasant without the summer traffic. Early September still has warm enough water for lake swimming and a noticeably thinner crowd.
Winter has its merits if you are a skier — the nearby resorts at Nassfeld (about 45 minutes by car) and Gerlitzen above the Ossiacher See offer solid skiing without the prices or queues of the more famous Tyrolean resorts. The Villacher Fasching carnival runs in the weeks before Lent (late January to early March, depending on the year) and is genuinely worth attending.
Villach has a relatively mild climate for its elevation, moderated by its position in the Drau valley and the Mediterranean air that flows through the gaps in the southern Alps. Summers are warm and occasionally humid; winters are cold but not extreme.