Set on a pass between the northern and southern sections of the Teutoburg Forest, Bielefeld is home to about 325,000 people. Sparrenberg Castle, one of the main attractions, dates from the 13th century, as do the Altstädter Nicolaikirche (St. Nicholas' Church) and the Neustädter Marienkirche (St. Mary's Church). The city also figures prominently in the Bielefeld Conspiracy, a German internet joke that the town does not actually exist, but is rather an elaborate alien or government conspiracy.