The Basilica Santuario di Maria Santissima del Suffragio in Grotte di Castro was built in 1625 by architect Girolamo Rainaldi and finished in 1672 by Andrea Selvi.
The church has a Latin cross plan and side chapels, enriched with priceless works: the painting of the Most Holy Crucifix between Sts. Francis of Assisi and Mary Magdalene, from the School of Guido Reni; the Baptism of Jesus, from the School of Pietro da Cortona; the Nativity of St. John the Baptist and the Beheading by Luigi Fontana; and the precious wooden statue of Our Lady of Suffrage from the early 17th century to whom the church is dedicated.

Located in twenty-four small rooms originally intended for the burial of the dead, it preserves a collection of sacred artworks as well as prehistoric and Etruscan relics. Sacred art objects include the reliquary of the Holy Cross and a chalice, donated according to tradition to the church by Pope Pius II (1462), and numerous votive offerings.
During work, which began in the mid-1960s, the pictorial and wall remains of the early church came to light, and the mummified remains of a woman (late 17th century) were found.