St. Hedwig's Cathedral is the seat of the archbishop of Berlin. It was built in the 18th century as the first Catholic church in Prussia after the Protestant Reformation by permission of King Frederick II. The intention of Frederick was to offer the numerous Catholic immigrants who had arrived in Berlin, especially those from Upper Silesia, a place of worship. The church was therefore dedicated to the patron of Silesia and Brandenburg, Saint Hedwig of Andechs. The building was designed by Georg Wenzeslaus von Knobelsdorff modeled after the Pantheon in Rome and construction started in 1747, interrupted and delayed several times due to economic problems. It was not opened until November 1, 1773 when the king's friend, Ignacy Krasicki, then Bishop of Warmia (later Archbishop of Gniezno), officiated at the cathedral's consecration.
After the Kristallnacht pogroms that took place over the night of 9–10 November 1938, Bernhard Lichtenberg, a canon of the cathedral chapter of St Hedwig since 1931, prayed publicly for Jews in the evening prayer following. Lichtenberg was later jailed by the Nazis and died on the way to the concentration camp at Dachau. In 1965 Lichtenberg's remains were transferred to the crypt at St. Hedwig's.
The cathedral burned down completely in 1943 during air raids on Berlin and was reconstructed from 1952 up to 1963.
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.