The former Franciscan monastery church "St. Crucis" is one of the most important preserved mendicant churches of Germany. With a length of 65 metres, it is also one of the largest examples of its kind in Thuringia. It was built in the 2nd half of the 13th century by using Romanesque components from its predecessor. After a sinkhole, the choir and a part of the south wall were rebuilt around 1350. The Gothic steeple dates from after 1400, and its dome was built in 1568. The monastery grounds belonging to the church originally stretched northwards to the inner city stream known as the Schwemmnotte.

After the Reformation, these buildings were completely removed. During the Peasants’ War in 1525 the church was the meeting place of the insurgents, and guns for the battle were also cast here. The Kornmarktkirche is therefore one of the most important sites for those events, which were highly significant for the history of the city.

The church was saved from demolition by its function as a parish church and by profane conversion since the early 19th century. Since 1975 it has been used as a museum, concert hall and conference venue. A permanent exhibition provides information on the period of the early Reformation and the Peasants’ War. Another exhibition focuses on the eventful architectural history of the former place of worship. In addition, a monastery garden laid out according to medieval models and a lapidarium with fragments of historical buildings invite visitors to linger.