The Episcopal Cathedral and Diocesan Museum extends over a floor space of 3000 square metres and is thus the second largest diocesan museum in Germany. It features a unique sequence of rooms from the early, high, and late Middle Ages in which works of art dating from 500 to 1500 CE are on display. The ground floor is reserved for special exhibitions. In the basement of the museum, visitors walk through early and late medieval vaulted cellars where artefacts of Roman Mainz, and the Romanesque and Gothic periods are exhibited. On the floor above the late Gothic cloister, a 800 square metre area houses sixty masterpieces of medieval and modern era art. The museum also includes St. Nicolas' Chapel with vestry where the cathedral's treasures are kept.
