The mosaics were created with over 41,500,000 pieces of tile in more than 8,000 shades of color, including gold. This is a view of the main altar and includes the baldachino or canopy above the altar, resting on marble pillars, and the ceiling dome illustrated with images of the 12 apostles.
This is one of the side chapels, the All Saints Chapel, I think, Below is a close-up of the altar in that chapel.
A basilica is a church that is designated by the Pope in part because of it's beauty. Pope John Paul II designated this cathedral as a basilica. These churches have symbols of papal authority including this umbrella or conopaeum and the small bell or tintinnabulum below which is used in the procession when the Pope is present.
The floors are beautiful mosaics, as well.
And this is part of the Italian-inspired geometric ceiling panels.
There is a recasting of Michelangelo's Pieta outside one of the chapels.
This is one of the newer mosaics in the ceiling depicts Jesus teaching his disciples.
This view of the ceiling is in the All Soul's chapel. Three bishops from St. Louis have been named cardinals. The cardinals' caps are hanging from their ceiling there. They will hang there until they totally deteriorate.
Another of the mosaic pictures.
One of the ceiling domes.
The altar in the Blessed Sacrament Chapel.