Prästö is an island in the municipality of Sund in the Åland Islands, Finland. It is connected to the Åland Mainland by the Bomarsund Bridge crossing the narrow Bomarsund Strait. Prästö is located next to the ruins of the Bomarsund Fortress, the place of the 1856 Crimean War Battle of Bomarsund. The island is known of its rich military history, especially of the six Russian military cemeteries established in the 19th Century. Because of the graveyards, Prästö was once known as the ″Island of the Dead″.