Yes, I’m sure I’ll visit many church, more perhaps than you want to read about. In this church, the Basilica Papale di Santa Maria Maggiore, I paid for a tour to see the mosaics. This post will feature mostly that part of the church.
However, first is an overview of the inside. The ceiling and high windows…
Some side aisles and features…
The one on the right had an feature of interest (a bit blurry, since I zoomed in a lot to get this)…

Of course, the floors are beautiful, too…

Finally, following signs I found the tour and joined it. All in the group were Italian except me, so I got a shortened version of the tour from the guide.
The angels guarding the mosaics (two on each end)…

The mosaics were created in two different time periods, first in the Middle Ages, showing Byzantine influence.

The original mosaics were on an open porch, but when they needed to be covered, the upper mosaics (earlier ones) were somewhat covered by the structure supporting the roof. On each side of Christ, area several of the early apostles and John Baptist, but really barely show today.
The lower mosaics…

Later, mosaics were add below the original. These featured several scenes of Mary and her life.
They also include the story of the building of the first church.
As the legend goes, two different people dreamed that they should build a church to Mary.
One asked for a sign, and on the 5th of August, it snowed on the hill where the church now stands.
You can see the white snow just above the shoulder of the angel.
Each August, white flower petals are dropped from the dome during mass to commemorate this miracle.
Finally, according to the guide, a magnificent marble staircase running up several floors was designed by Bernini. It has no visible means of support except for the steps placed inside the walls. I enjoyed getting the face of a lovely young Italian girl as she explored the staircase, although she apologized for getting in my way.