Reso, Sweden offers 1 beach perfect for sunbathing, surfing, swimming, and more. Reso, Vastra Gotalands lan, Sweden, is known for the Kosterhavet National Park. The best time to travel to Reso, Sweden, is during the summer months of June to August, when the average air temperature is around 15-20°C (59-68°F) and the water temperature is approximately 15°C (59°F). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!