The Cattedrale di San Cassiano is a Baroque cathedral and minor basilica dedicated to Saint Cassian of Imola, the patron of the town. The current structure dates from the early 18th century, built over an earlier medieval church and substantially rebuilt in 1748. The interior is restrained by Italian Baroque standards — a single nave, white walls, and a modest set of side altars — but the facade is handsome and the bell tower visible from most of the town's canals.
The cathedral sits on the southern side of the main square, Piazza XX Settembre, which is the social heart of Comacchio. In the evening, chairs appear outside the bars bordering the square and the whole town seems to gather here. Worth a look inside for the carved wooden choir and the 18th-century reliquary; the sacristy sometimes displays pieces from the town's earlier ecclesiastical collections.