The Church of San Julián y Santa Basilisa stands in the village of Isla, municipality of Arnuero, as one of the finest examples of classicist architecture in Cantabria. Built between 1685 and 1690 under the patronage of Archbishop Juan Fernández de Isla, its design is attributed to master stonemason Francisco del Pontón Setién.
The church follows a hall plan with three naves of equal height—the central one wider—supported by cylindrical pillars with Tuscan capitals. The main altarpiece (1689-1697) is a monumental Baroque piece featuring polychrome Solomonic columns and reliefs depicting the life of the Virgin Mary.
Among its most remarkable treasures is a Romantic English organ from around 1890, unique in Cantabria, separately declared a Cultural Heritage Asset. The church itself was declared BIC (Monument) in 2002.
Open Tuesday to Sunday (10:00-13:30 and 16:00-19:30), entry 1 euro. Part of the Ecoparque de Trasmiera heritage trail, alongside nearby Monte El Cincho and Isla's beaches.
