Kosterhavet
Sweden's first marine national park: deep-water fjords, eelgrass meadows, and the Koster islands.
Kosterhavet, opened in September 2009 as Sweden's first marine national park, is a park you mostly can't see: nearly four hundred square kilometres of Skagerrak around the Koster islands, from sunlit eelgrass shallows down into the Koster Trench, a submarine valley reaching 247 metres. Through that trench flows genuinely oceanic water — salt, cold and stable — which is why these are the richest waters in Sweden: some 12,000 marine species, a couple of hundred of them found nowhere else in the country, including Sweden's only living cold-water coral reef, Lophelia pertusa, at the trench's dark bottom.
The border matters here in a good way. On the Norwegian side the same waters are protected as Ytre Hvaler national park, opened the same year; together the two form a single protected sea across the frontier, the first arrangement of its kind in Scandinavia. The other unusual arrangement is human: Kosterhavet was designed with its fishermen rather than against them, and the Koster shrimp fishery continues inside the park under negotiated rules — a working fishery inside a national park being a small piece of policy that much of Europe comes to study.
Above the waterline, the Koster islands themselves (mostly nature reserve rather than park) supply the postcard: car-free, granite-shored, bicycle-laced, with fishing villages and swimming coves in Bohuslän's best manner.
What's worth knowing before you go
The gateway is Strömstad — easy by train from Gothenburg — with the Koster ferries making the crossing in under an hour. On Sydkoster, the naturum at Ekenäs is the park's front door and its aquarium the only comfortable way to meet the trench fauna; snorkel trails, seal safaris and guided low-tide walks cover the shallower registers. Bikes rule the islands; book beds early in July. The season is long — May and September are lovely and far calmer.
The connoisseur's detail is edible: Koster shrimp, landed by the boats the park was designed around, eaten by the harbour they came into. That is the management plan, on a plate.