The Porvoo Cathedral was originally made of wood. The first stone walls were built between 1410 and 1420 and in 1450 the church was expanded four meters towards east and six meters towards south.
The cathedral has been destroyed by fire numerous times; in 1508 by Danish and in 1571, 1590, and 1708 by Russian forces. On May 29, 2006, the outer roof collapsed after arson, however with the inner ceiling undamaged and the cathedral interiors intact. The Cathedral was reopened on 2 July 2008.
Porvoo Cathedral is situated in the middle of Porvoo well-preserved and beautiful old town, which is popular tourist attraction particurarly in summer season.
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.