The Roosna-Alliku Manor was donated to von Rosen family in 1620 by Christina, Queen of Sweden. The coat of arms of family features a white rose, which has become the symbol of the manor. In 1721 it was acquired by von Stackelbergs. The present main building is one of the most impressive examples of early classical manor architecture in Estonia, completed by Otto Friedrich von Stackelberg in 1786. Worthiest of attention in the interior are the two rooms with artificial marble walls. The manor building has been a school since 1924. Visits during the school period are possible by appointment only.
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.