Château de Cajarc, built in the 13th and 15th centuries, is an well-preserved example of mediaeval fortification. Especially noteworthy are the roofs, the round tower and its staircase and the inner courtyard and its walls. On the second floor, a vaulted room contains 17th-century paintings.
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.