In the midst of narrow streets in the heart of Stampace, a medieval district of Cagliari, stands the church from where one of the oldest religious celebrations in Italy and the most engaging of the island set out each 1st May, being the Festa di Sant’Efisio. The original building dates back to the 13th-century, constructed over a grotto that opens into the limestone to a depth of nine metres, considered by the local faithful as being the prison in which Efisio was locked up before being martyred and beheaded on Nora beach (303 AD). The church was expanded and modified in 1538, when the oratory was built alongside, perhaps designed by the Piedmont architect De Vincenti, who was working in Cagliari at the time on the restoration of the former Collegio Gesuita di Santa Croce. At the end of the 18th century, new operations conferred the present appearance of the church, typical of the 18th century Piedmontese Baroque style. The reconstruction was completed in 1782.

The church of Sant’Efisio overlooks a small piazza in which the rooms of the Archconfraternity of the Gonfalon, dedicated to the saint’s worship, overlook. Alongside is a narrow street that flanks the parish church of Sant’Anna. At the centre of the simple façade, marked by three orders of Ionic pilasters, is the portal bordered by two false niches. Over a window. The order crowning is a curved tympanum topped in the form of an ‘old-style Admiral’s hat’ framed by twin mouldings that meet in two volutes joined by a garland. The decoration in Piedmontese style recalls that of the nearby church of Santa Restituta, built a century earlier and the model for many Sardinian churches. Rising up on the right-hand side is a bell tower surmounted by a small dome covered with majolica, with the reconstruction dating back to the 16th-century. Within, on a single wide barrel-vaulted nave, open up three chapels on each side. The presbytery is raised and covered by a dome. The room is marked by classical decorations, such as pilasters and trabeations. The furnishing is typical of the late-18th century, especially the high altar in polychrome marble (1786). In the centre is a gilded wooden tabernacle in the shape of a temple, containing the relics of the warrior martyr. In a chapel to the right is preserved the 17th-century statue carried in the procession held on 1st May, whilst in the chapel dedicated to him is a second beautiful processional statue of the saint, by Giuseppe Antonio Lonis (1755), carried each Easter Monday to the cathedral of Santa Maria to thank the saint for defeating the fleet of French revolutionaries. Also within is a third 16th-century statue named Sant'Efis Sballiau (‘mistaken’), as it depicts him with the palm of martyrdom on his right hand instead of on his left, as shown in the iconography. The nave is joined by the body of the large Cappella del Crocifisso, which can be accessed from the third arch on the right. A large canvas depicting the conversion of the saint stands in the centre of the vault. Other valuable works include a number of paintings and an Ecce Homo, a 17th-century sculpture characterised by great expressionism.

A steep staircase carved into the rock leads to the crypt, traditionally the Efisiu Gloriosu prison. In Roman times, the hypogeum was likely used as a temple dedicated to the goddess Isis. A well in the middle of the floor would have contained the water for initiation rituals. In 1616, a tomb with a skeleton believed to be that of Sant'Edizio was discovered. Confirmation came from a marble slab on which was written bonae memoriae Editius.