Enholmen, Military fortress island near Slite, Sweden

Enholmen is a small island in the Baltic Sea featuring the remains of Karlsvärd Fortress with stone structures that face the water. The ruins still show the basic layout of a former military fortification today.

A five-sided bastion fort was begun on the island in 1657 but abandoned after a few years. Work resumed in 1711 under the name Karlsvärds fästning, built in four phases and completed only in 1771 to protect Slite, eastern Gotland's main harbour. The fort was abandoned in 1788, leaving parts of the bastions and ramparts.

The island served as a quarantine station during the 1830s cholera outbreaks to protect public health in the region. This shift in purpose shows how the site adapted to meet the needs of the time.

Enholmen is a state building monument since 1935 and was a military protection area until the late 1990s, so access was long restricted. Visitor tours to the island have been organised since 2014. The island lies just off Slite in northeastern Gotland, and the cholera cemetery is on a peninsula on its western side.

The two curved stone batteries finished in 1858, with eight 24-pounder and sixteen 7-inch guns, are the only surviving example of this mid-19th-century fortification type. They were decommissioned in 1905. Look for the firing positions on the shores, traces of the island's manning during the world wars.