It's a cave, partly natural and partly hollowed in the rock, that dates back to the Punic-Roman and early Christian Ages.  The interior consist of numerous rooms characterised by an irregular shape and used as altars or reservoirs.
It's dedicated to St. Eusebius' mother, bishop of Vercelli, victim of the Diocletian's persecutions.  The cult of S.Restituta is of African origin.  It seems that the relics arrived on the island about the V Century and were collected in an earthenware pot.  After their discovery in 1614, a niche was opened in the wall in order to set the Saint's simulacrum.
Another small crypt conserves the massive stone column used during the martyrdom.  Other stone altars, quite rudimentary, were built and decorated on the frontispiece.
During the 1943, the crypt was used as air-raid shelter by the population, as evidenced by the inscription on the memorial tablet.