Gutenfels Castle was built in 1220. It was used with Pfalzgrafenstein Castle in the middle of the Rhein and the fortified town of Kaub on the far side to provide an impenetrable toll zone for the Holy Roman Emperor until Prussia purchased the area (1866) and ended this toll in 1867.
This castle, primarily owned (since 1257) by the Falkenstein family, is one of the most important examples of the Hohenstaufen military and house construction style at the Rhine. Since 1277 it has been a castle of the Electorate of Palatinate. After an unsuccessful siege in 1504 by landgrave Wilhelm from Hessen, the castle was renamed Gutenfels (solid rock). Rebuilt between 1889 and 1892 it is now used as a hotel.
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.