The oldest city church is "Altstädter Nicolaikirche". It is a Gothic hall church with a height of . It was founded in 1236 by the Bishop of Paderborn, and enlarged at the beginning of the 14th century. The church was damaged in World War II and later rebuilt. Three times a day, a carillon can be heard. The most valuable treasure of this church is a carved altar from Antwerp, decorated with 250 figures. A small museum housed within illustrates the history of the church up to World War II.