In the right nave there are three Baroque chapels dedicated to Saint Fulgenzius and Saint Dominic, as well as a baptistery. The first chapel, which contains the relics of Otricoli’s proto-martyr, features a beautiful wooden cupboard decorated with gilded faux-marble motifs (1717) and a fresco depicting St. Fulgenzius distributing bread to the poor of Otricoli. The second chapel houses a fine altarpiece and 17th-century frescoes. Next to the entrance is the Baptism Chapel, with a 16th-century marble baptismal font, an interesting 13th-century marble tabernacle, and remains of frescoes ranging from the 14th to the 17th century.

In the left nave there are two beautiful Baroque chapels: the small chapel dedicated to Saint Anthony Abbot and a “passing chapel” dedicated to Our Lady of Sorrows. The first, known as Cappella del SS. Sacramento (Chapel of the Most Holy Sacrament), is of Gothic origin but was completely rebuilt in the 16th century; its dome features a fresco depicting Vision of Saint John on Patmos and the Angel of Fire, painted by Filippo Ralli between 1722 and 1727. In the second chapel, visitors can admire a reliquary altar with sixteen frescoes framed in stucco and gilded decorations, illustrating the Mysteries of the Holy Rosary and episodes from the Virgin’s life. In the chapel of Our Lady of Sorrows, noteworthy features include frescoes dating to the first half of the 16th century and the Dove of the Holy Spirit within a radiant halo, a 17th-century work in polychrome stucco.

The main altar, a simple structure of Umbrian workmanship dating to the 12th-13th century, is enriched by a splendid 16th-century marble ciborium supported by reused Roman columns. At its base is the Fenestrella Confessiones, while below lies the Romanesque crypt dedicated to Saint Medico. Above, at the centre of the apse wall, stands a masterpiece of contemporary stained glass by the Otricoli-born artist Roberto Marini; beneath it, arranged in a horseshoe shape, is a precious 15th-century wooden choir adorned with fine inlay work.

In addition to the many fine altarpieces from different periods, the church also houses stone materials uncovered during 20th-century excavations, originating both from the building itself and from the ancient city of Ocriculum. These include friezes from funerary monuments, capitals and pulvinos, inscriptions, fragments of sarcophagi, fragmentary sculptures, slabs and pieces of ciboria. Together with its long and complex history, this rich collection makes the Collegiate Church of Santa Maria a true historical museum of the city.