Brynolf Algotsson, Bishop of Skara, laid the foundations for a fortified castle in Läckö in 1298 originally as a fort that consisted of two or three houses surrounded by a wall. After a fire during the 1470s, the fort was expanded by bishop Brynolf Gerlachsson.
After the reformation in 1527, King Gustav Vasa took possession. Field Marshal Jacob Pontusson De la Gardie was granted the property in 1615. Field Marshal de la Gardie embarked on an extensive building spree, including the third floor of the keep. The portal to the main courtyard was added during his period, as were the frescos depicting people and winding plants found in niches, stairwells and the rooms on the third floor. In 1654, Count Magnus Gabriel De la Gardie initiated immense construction projects at Läckö. A fourth floor was built in the main building and a number of artists were hired to decorate the walls and ceilings of the castle.
Läckö Castle is a national monument and has been managed by the National Property Board since 1993.
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.