Situated at the junction of the Quays of the Boatmen and the Quays of the Fishermen, the Church of Saint-Guillaume is remarkable for its picturesque location on the banks of the Ill, its rich interior decor combining Gothic and Baroque styles, and above all its exterior facade which appears crooked.The first church, built at the beginning of the 14th century , was Catholic and was a brick, unvaulted building with a single nave extended by a polygonal choir. This layout corresponded to the ideal of the mendicant monks, the Guillemites, who occupied the parish until the Protestant Reformation of the 15th century.In 1667, having become a parish church, Saint-Guillaume acquired a bell tower, radically transforming the old façade with three gables and triangular windows. The old porch, which followed the street's layout, actually has a trapezoidal plan: the new porch and its bell tower then appear to be asymmetrical and askew.