Here are 2 photos of random ceilings along the way:
St. Peter's Basilica is (perhaps) the largest in the world and holds up to 50,000+ people. It covers over 5 acres. The top of the dome, designed by Michelangelo, is over 400 ft from the floor. A lot of the columns and artwork found here were actually taken from other sites and "repurposed" here. I found it amazing, not so much for it's religious significance, but more for the intricate tile floors, mosaic artwork, Michelangelo's sculptures, etc. A magnificent place! The whole Vatican museum is more like an art gallery than a church.
A photo can't do justice to the scale and beauty of this place: