Stegeholm's Castle Ruin is located on Slottsholmen by the mouth of Gamlebyviken. The oldest notes about Stegeholms castle are from the 14th century. It was probably built before 1370 by Albert II, Duke of Mecklenburg (the father of King Albert of Sweden). The castle was destroyed by fire in 1517 and rebuilt in 1521. In 1612 it was conquered by Danish. The final destruction appeared in 1677 when Stegeholm was destroyed by Danish-Dutch fleet. Today Västerviks Visfestival (Song festival) is organized in the castle ruins annually.References:
The Petersberg Citadel is one of the largest extant early-modern citadels in Europe and covers the whole north-western part of the Erfurt city centre. It was built after 1665 on Petersberg hill and was in military use until 1963. It dates from a time when Erfurt was ruled by the Electors of Mainz and is a unique example of the European style of fortress construction. Beneath the citadel is an underground maze of passageways that can be visited on guided tours organised by Erfurt Tourist Office.
The citadel was originally built on the site of a medieval Benedictine Monastery and the earliest parts of the complex date from the 12th century. Erfurt has also been ruled by Sweden, Prussia, Napoleon, the German Empire, the Nazis, and post-World War II Soviet occupying forces, and it was part of the German Democratic Republic (East Germany). All of these regimes used Petersberg Citadel and had an influence on its development. The baroque fortress was in military use until 1963. Since German reunification in 1990, the citadel has undergone significant restoration and it is now open to the public as a historic site.