Château de la Guerche was built during the reign of Charles VII of France, for Antoinette de Maignelais, young cousin of Charles's recently defunct mistress Agnès Sorrel, and her new husband André de Villequier.
The castle was besieged in 1592, during the French Wars of Religion. Restored in the seventeenth century and renovated subsequently, it is now open to visitors.
References: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.