The Cathedral of Saint Blaise (Dom St. Blasii) dominates the southern end of Burgplatz, its twin-towered Romanesque west front dating from the 12th century. Inside, the nave is broad and light, with a notable 12th-century chandelier — the Heziloleuchter, a hoop-shaped bronze candelabrum — hanging above the crossing.
The tombs of Henry the Lion and Duchess Matilda lie in the crypt beneath the high altar; the carved stone effigies are among the finest surviving examples of 13th-century German funerary sculpture. The cathedral treasury contains medieval reliquaries and goldwork from Henry's collection, including pieces thought to have come from Constantinople. Entry is free; the crypt and treasury require a small additional fee.