Just outside the walls of the castle of Mondolfo appears the Complex of St. Agostino, which consists of a wide convent dating back to the 17th century and the majestic 16th-century church of St. Maria (dating back to the 15th century), better known as church of St. Agostino, whose first notes take us back to the end of 13th century.

The complex is an important cultural center, where two large rooms can be used for conferences, cultural meetings etc.

Along both sides of the church there are twelve carved wooden or carved stone altars, in addition to the apsis and the chapel restored in the 18th century. Three portals lead into the wide renaissance nave and the church has been described as a true picture gallery due to the works of important painters of the first half of 17th century.

After the third altar to the left you can see a pulpit with gilded wooden canopy and to the right the chapel of St. Nicolas of Tolentino, where canvas of St. Nicolas (by an unknown painter who lived at the end of the 17th century), The miracle of the procession in time of plague and Madonna and Child with Saints Nicolas and Francis can be seen. They were painted by the artist from Bologna, Alessandro Tiarini (1577-1668), who in his works combines naturalism and intense pathos, according to the Counter-Reformation painting guidelines.

All the paintings of the church are noteworthy. Behind the first altar to the right hangs a copy of Barocci's Madonna della Gatta, a painter (1535-1612) known for his sweet nuances and infusing devotion, a work of art which was made in the workshop of the artist himself.

Above, in the early 16th century lunette of Umbria-Marche school the Madonna and Child with two worshipping angels are represented. Behind the third and fourth altars hang two paintings by Claudio Ridolfi from Verona (1570-1644): St. Anthony Abbot and Paul the Hermit (after 1621) and Madonna and Child with the Saints John the Baptist and John the Evangelist. At the fifth altar the painting of the Martyrdom of Saints Simon and Jude is signed and dated 1649 by Giovan Francesco Guerrieri (1589-1657), an artist whose painting is characterized by a deep religiousness, a sharp luministic contrast and a naturalistic approach to the subject. Behind the sixth right altar hang fifteen small paintings by an anonymous 17th century artist from the Marche representing the Mysteries of the Rosary. They surround a 16th-century painting in Byzantine style,Our Lady of Good Counsel.

In the left altars as well as in the apse there is a painting by the Flemish Ernst Van Schayck and by the artists Giuliano Presutti and Sebastiano Ceccarini from Fano.

Other works: polichrome sandstone Piet from the 15th century, magistrate's bench (16th century), richly carved wooden choir and sacristy.

The 17th-century cloister is adjacent to the church. It has a well in the centre and along the perimeter of the small arches there are frescoes representing the life of St. Augustine.