The concattedrale of the Immaculate Conception is the cathedral of Bosa. The building is located in the historic city center, at the height of the nineteenth-century bridge. The façade is divided into two orders, from an entablature very similar to that of the church of the Madonna del Carmelo. The first order is enriched by curves and lively shapes, characterized by the hat that overhangs the portal. The upper order, enlivened also has a window in the middle with the image of the immaculate and, concludes with a soft gilt in red vulcanite. The internal structure consists of a single nave, on it open eight chapels, including the transept in turn divided into 4 smaller chapels and, from an altar with a larger dome than the other altars, for this is also called ; chapel of the Sacred Heart. The chapels of the transept are dedicated to Saint Joseph, to Our Lady of Bonaria, to the souls of Purgatory. The side walls of the nave are divided into four spans of semi-columns with rich capitals on which rests a continuous trabeation on which stands the 17-meter high barrel vault divided into 10 lunettes to which 10 windows. The eight chapels are dedicated to: Sacro Cuore, San Francesco Saverio, Sant'Anna and the Santissimo Crocifisso. The latter in polychrome stuccowork was made by Carlo Antonio Ferrara and at the top shows the coat of arms of the municipality of Bosa that took care of the financing of the construction of the chapel. In the niche there is a crucifix, the sixteenth century polychrome wood nailed to a cross only designed in stucco. The last chapel on the right side serves as an entrance to the sacristy. The chapels on the other side, starting from the presbytery, house: the first the side entrance with the nineteenth-century compass, the second the sorrow, the third San Giovanni Nepucomeno, whose polychrome wooden statue dates back to the second half of the 1700s. chapel houses the eighteenth-century statue of the Madonna del Carmelo and in the last there is the baptismal font in marble, this chapel also houses a painting depicting the Batesimo of Christ. The wide marble staircase gives access to the large presbytery. In the side walls of the presbytery not made in wall tempera, as well as all the other decorations of the church, two large paintings, one representing the visitation and the other the annunciation. Continuing with the paintings we have the huge apsidal basin in which are depicted the patrons of the city, Emilio and Priamo, on the sides of the town, which contemplate the virgin Immaculate assisposed on the clouds between musicians and singers angels. Underneath the basin there are two large paintings of the minor patrons, San Sebastiano and San Rocco, also by Scherer but recently ruined by poor inexperienced hands. In the large semicircular choir there is a precious image of Santa Maria de Gratia, a sixteenth-century polychrome sculpture with a gothic structure that shows a quotation from the cantico of the cantici on the pedestal "(dil) exit me rex et introduxit me in cubiculum. The raised presbytery is surmounted by a high dome on an octagonal drum set on plumes, designed in the early nineteenth century by the architect and ornatist Domenico Franco. Last important detail of the cathedral are the two statues of Saints Peter and Paul on the sides of the altar. These two simulacra of 1608 come from the ancient cathedral of San Pietro extramuros where they were kept in two niches and were exhibited on the occasion of the feast. Of probable attribution to the Spanish sphere they were restored for the first time in 1948, then in 1974 during which the pedestals bearing the inscriptions were stolen. It is from these inscriptions that it is assumed that they were donated by Antonina Maiali.