Grad Sibenik, Croatia offers 5 beaches perfect for sunbathing, surfing, swimming, and more. Grad Sibenik is known for the UNESCO World Heritage Sites of St. James Cathedral and St. Nicholas Fortress. The best time to travel to Grad Sibenik, Croatia, is from May to September, when the average air temperature is around 75°F (24°C) and the sea temperature is approximately 73°F (23°C). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!