Asunden, Natural heath in Gotland, Sweden

Asunden is an uninhabited island off Slite on northeastern Gotland, about two kilometres long and one kilometre wide. Its east side holds a nature reserve with over 25 rauks taller than two metres, the highest reaching nine metres. The limestone was formed as a coral reef some 430 million years ago.

Asunden served as a military protected area until the late 1990s, when the landing ban was lifted. A coastal artillery battery of three guns once stood here, two on Asunden and one on Hammarlandet to the north. The rauk field on the east side was designated a natural monument in 1930 and became a nature reserve under the 1964 Nature Conservation Act.

The name Asunden is shared with several Swedish lakes, and the island lies just off Slite, northeast of Enholmen and Grunnet. Its beach meadows on the northwest shore are part of Natura 2000 and draw birdwatchers; species recorded breeding there include ruff, common tern, Arctic tern, pied avocet, little tern and dunlin. The rauk area was protected as a natural monument in 1930.

The area is accessible year-round and can be explored on foot. Temperatures range from about 16°C in summer to around 0°C in winter, so dress accordingly for your visit.

The limestone of Asunden is a fossil coral reef formed in a tropical sea about 430 million years ago, in the Silurian. It is rich in fossils such as stromatoporoids, and the harder reef limestone survived erosion to become the rauks.