The crypt of Saint Efisio is located beneath the omnymous church, in a cave about nine meters deep, where according to the tradition, the martyr Efisio was imprisoned before being beheaded in Nora in 303 AD. Here, can be admired an altar decorated with glazed ceramics from the 17th century and the column to which the saint was tied up and tortured. The small cave is a place of great worship by the inhabitants of Cagliari, who celebrate the saint every 1st of May, when the statue is solemnly brought in procession to Nora.