The Cathedral of the Assumption of Mary is one of the most important Romanesque buildings in Germany and a UNESCO World Heritage Site since 1985. Built under Bishop Bernward in the early 11th century and extensively rebuilt after destruction in 1945, it contains a treasury of medieval metalwork that is astonishing in its density: the famous Bernward Doors, the Christ Column (a bronze pillar 3.8 metres high, wound with scenes of Christ's ministry like a miniature Trajan's Column), the Hezilo chandelier, and the Bernward Cross all survive from the original building.
The cloister attached to the cathedral is the home of the Tausendjähriger Rosenstock — the thousand-year-old rose bush that clings to the apse wall. According to local legend, the cathedral was built on this spot after Louis the Pious found his hunting party lost in a snowstorm and discovered a rose bush blooming miraculously in February. The bush is certainly ancient; it was badly damaged in the 1945 bombing but survived, flowering again from the roots the following year.