The Seminary building is a construction of the late eighteenth century was opened in 1788. Although the author is unknown, it is sometimes referred to the workshop of Luigi Vanvitelli (1700-1773); it arose on some Sandri family houses and other privates, purchased for this very purpose, over several decades, using the assets of the suppressed monastery of St. Stephen.

It now has a three storey facade, divided into five bands, the middle one slightly overhanging; to the left, perpendicular to the main body of the factory, advances another band, where the chapel and the headquarters of the former library lie. Inside there follow some salons, which once served as a studio and dormitory for seminarians, while on the top floor and at the back there are the rooms of the professors and many service quarters.