Veste Niederhaus is located below on the bank of the Danube. It is connected to a larger Veste Oberhaus castle by a battlement; this addition, made after 1367, created a double fortress almost 700 metres in length.
Bomarsund fortress and garrison was built in 1832-1854 by Russian Empire to defence Åland Islands against enemies. British and French fleet attacked against it during the Crimean War in 1854. After a week of fighting the British stormed the remaining fort. Anglo-French forces destroyed it totally after battle. In the Treaty of Paris 1856, the entire Åland Islands were demilitarized, which is a status that has been preserved until this day.
Nowadays there are some ruins left and fortress area is open for visitors.