The Cathedral of Saint-Étienne is the centrepiece of Auxerre's skyline, visible from across the valley. Construction began in 1215 and continued for over three centuries, leaving the facade incomplete — the south tower was never finished, giving it an asymmetrical outline that local historians have argued about ever since. The interior is famous for its 13th-century stained glass, among the finest in Burgundy, particularly in the choir ambulatory.
The crypt is separately ticketed and worth the extra cost: it contains a late-Antique fresco of Christ on horseback — rare, early, and genuinely startling. Free to enter the main body of the cathedral; crypt admission around €3.