The architect of this now deconsecrated 19th-century French-built cathedral employed an unorthodox mix of Moorish, Byzantine and Gothic architectural styles in its design, and the result sits somewhat uncomfortably atop symbolically loaded Byrsa Hill. The interior has been restored and is now used for exhibitions and concerts (hence the name change); it's not really worth paying the inflated fee to visit at other times.
The cathedral was dedicated to the 13th-century French saint-king Louis, who died on the beach at Carthage in 1270 during the ill-fated Eighth Crusade (he was hoping to convert the Hafsid ruler; instead his troops wilted in the heat).