Mustio manor ("Mustio Castle", "Svartå Slott") was built in 1783-1792 by Magnus Linder, the owner of the local ironworks. There had been an older manor from the 17th century, but it was dismantled when the present one was built. The manor represents the neoclassical ("kustavilainen") architecture.
Today Mustio is a countryside hotel. There are also the old ironworks and one of the biggest private historical parks of Finland.
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.