Kosterhavets Nationalpark.

Sweden’s first marine national park protects a sprawling underwater wilderness of deep fjords, cold Atlantic currents, and exceptional salinity. This unique environment supports over 6,000 marine species, including hundreds found nowhere else in the country, alongside Sweden's largest colony of harbor seals. Instead of a sterile reserve, this is a living, working seascape where regulated local fishing coexists with conservation. Visitors typically start at the Naturum visitor center on the car-free island of South Koster, reached via a scenic 45-minute ferry ride from Strömstad. From here, the park is best experienced on or below the water—whether by kayaking through the granite archipelago, hiking the wind-swept shoreline, or snorkeling above the rare cold-water reefs.