The Bomarsund Fortress () is one of the most interesting historical places in Sund. After Sweden lost the Finnish War of 1808–1809, fought against Russia, both Åland and Finland became part of the Russian Empire. Russia began to build a fortress in Sund in 1830 in accordance with the orders of Emperor Nicholas I. People of various cultural backgrounds came to Sund from all over Russia to build the fortress. A town, Gamla Skarpans, was built and another settlement, Nya Skarpans, was established inside the fortress. However, the fortress, designed for 5000 men and 500 cannon, was never finished: in 1854 during the Åland War, part of the Crimean War, British and French troops invaded and blew it up in the Battle of Bomarsund. Today, in addition to the fortress, there are the ruins of Gamla Skarpans and two watchtowers nearby, all open to visitors. The island of Prästö is located next to the Bomarsund Fortress. The island is known for its six Russian military cemeteries and for two museums show-casing the history of Prästö and Bomarsund.