The Romanesque and Gothic St Mary's Cathedral, built between the 9th and 14th centuries, features impressive frescos, an 11th-century bronze portal (now at the Diocesan Museum), a Romanesque crypt, and four panel paintings by Hans Holbein the Elder. 

Twelfth-century windows displaying the prophets are said to be the oldest stained glass windows in Germany depicting figures. Many finds from the Roman era to be seen on the square.