The archipelago in the Baltic Sea between Åland and mainland Finland is one of the largest archipelagos in the world. The National Park includes more than 2,000 islands and rocky islets shaped by waves and the ice 
sheet during the Ice Age. Inside the co-operation area of the park, there are about 8400 islands and islets altogether. The National Park mostly consists of outer archipelago, characterised by windswept pine forests (Pinus sylvestris) on the rocks, low deciduous forests and bare rocky islets which show parts of the 2,000-million-year-old bedrock. However, between the rocks there are hollows with lush vegetation of great diversity.
Due to the salinity in the brackish water (in the Archipelago about 5-6 per mil), the number of different species living under water is low, but because of abundance of populations of the species, the sea is filled with life.
Large areas of open sea, brackish water, bare outer islets and lush herb-rich forests create the habitat for diversity of plant and animal species. A special feature of the National Park are traditional agricultural landscapes, such as leaf fodder meadows, wooded pastures, dry meadows, coastal meadows and heaths, where the cattle of the inhabitants of the archipelago grazes. There are about 3 sq.km. of traditional agricultural landscapes in the National Park. The goal of the National Park is to protect the ecosystems and the culture of the Archipelago and the traditional ways of utilising the nature, to preserve the communities of the archipelago, and to promote environmental research.
Plants
The exceptional diversity of the vegetation at the Archipelago Sea arises from the small features of the landscape, and the variety of rock basement. Although the park for most part consists of bare and rocky outer islands, calciferous soils nourished by shell remains and deposits of limestone can support luxuriant groves between the rocks. For example, ash (Fraxinus excelsior) often grows in the hollows.
Around dry pasture meadows grow the Bloody Cranesbill (Geranium sanguineum) and the Swallowwort (Vincetoxcium hirundinaria). On leaf fodder meadows bloom the Elder-flowered Orchid (Dactylorhiza sambucina) and the Nettle-leaved Bellflower (Campanula trachelium), and on the edge of the forest grow the Common Buckthorn (Rhamnus catharticus), and the Crab Apple (Malus sylvestris).
Animals
In the Archipelago area live 25 species of mammals, the most common ones being small rodents. Also large animals, such as mooses (Alces alces), can be seen. Most part of the declining population of the Baltic Ringed Seal (Phoca hispida botnica) in the archipelago lives inside the National Park. The Grey Seal (Halichoerus grypus ) is becoming more common, and it may turn up to watch boaters almost anywhere in the National Park.
There are 132 breeding bird species in the Archipelago. Gulls (Larus), arctic terns (Sterna paradisaea), eiders (Somateria molissima), razorbills (Alca torda) and black guillemots (Gepphus grylle) nest on small bird islets. The mute swan (Cygnus olor), greylag goose (Anser anser) and shelduck (Tadorna tadorna) build their nests in the peaceful archipelago, while the arctic skua (Stercorarius parasiticus) looks out on the high rocks.
The nutcracker (Nucifraga caryocatactes) and barred warbler (Sylvia nisoria) live in the shelter of leafy trees. These days it is also possible to see the white-tailed eagle (Halliaeetus albicilla) gliding up in the sky. It has been saved from exctinction by active conservation measures. Threatened species in the area include the caspian tern (Sterna caspia) and a subspecies of the Dunlin (Calidris alpina schinzii).