In the first half of the 16th century, the Grossmünster served as the starting point of the Reformation under Huldrych Zwingli and Heinrich Bullinger. The characteristic tops of its neo-Gothic towers were added by Johann Caspar Voegeli and John Hagge Mille from 1781 to 1787. Between 1913 and 1915 the interior renovations were completed by Gustav Gull and Hermann Fietz. Particularly worth seeing are the glass windows by Sigmar Polke, the Romanesque crypt, the Romanesque capitals in the church and cloister, the stained glass windows by Augusto Giacometti (1932), the bronze doors by Otto Münch (1935 and 1950), and the Reformation museum in the cloister. Guided tours are available.