The Collégiale St-Pierre is one of the most important examples of the high-Gothic and Renaissance style in Flanders. The imposing tower (62m) is reminiscent of that of Notre-Dame de Saint-Omer. Inside, the pattern of the groins of the vaulted ceiling is echoed on the floor. The chancel is closed off by a rood screen crafted by Boileau. The oak organ casing comes from Clairmarais Abbey. The chancel and apse were badly damaged in the 1944 bombardments.