The Cathedral is home to the largest collection of mosaic art in the western hemisphere, probably the world – mosaics literally cover the walls. Construction of the church began in 1907. In 1997, the Cathedral was designated a Cathedral Basilica by Pope John Paul II. He honored the Cathedral Basilica with a visit during his history-making visit to the United States, in October of 1999. The Cathedral is open daily for masses and self-guided tours.
The lower level holds the Mosaic Museum, containing displays showing how mosaics are designed and applied. The museum contains the original Kilgen organ console; the throne used during the visit of Pope John Paul II; and a collection of historic vestments and precious objects used in the various rites of the Church. Admission to the museum is $2.
There is a crypt where the remains of Saint Louis's Cardinals and Archbishops are interred. The needlepoint prie-dieux in the crypt were created by members of the parish for the use of Pope John Paul II during his 1999 visit.