September is widely considered the best month to visit Croatia in 2026. By September, the intense "heat domes" of July and August have dissipated, leaving pleasant daily temperatures around 24°C–26°C. Most importantly, the massive summer crowds have thinned out, meaning you won't be fighting for space on the Stradun in Dubrovnik or at the Plitvice Lakes waterfalls. The Adriatic Sea remains warm enough for swimming (around 22°C) throughout the month. Additionally, September marks the start of the truffle and wine harvest festivals in Istria, providing a rich cultural experience. Prices for accommodation and ferries also begin to drop to "shoulder season" rates, often 20–30% lower than in August. If you prefer the start of the season, June is a close second, offering long daylight hours and lush green landscapes, though the water can still be a bit "refreshing" for some swimmers.