The most interesting and valuable monument not only for Fonni but for the whole area is the Basilica of the Most Holy Virgin of Martyrs, erected as a national monument , attached to the convent. It is a unique church complex in Sardinia with a great essentiality of lines, rich in precious ornaments and consisting of a very interesting crypt. Inside, it is possible to admire one of the wall paintings of the 1700s that contributes to determine a remarkable expressive vivacity; other devotional “messages” were executed with medieval and Renaissance forms of painting that add to the Baroque and late Baroque iconographic contributions. The shrine was inaugurated by Father Pacifico Guiso Pirella in 1708.