San Crisogono is an underground site in Trastevere which could definitely use some improvement in their explanations of what you're seeing in the underground. I don't recall anything about the church; I went straight for the underground. Although the signage in the underground is not very good, there is at least a pamphlet that's given to you to help you figure out what you're seeing underground. Still, the tourist experience could easily be greatly improved with a better English pamphlet or English underground signage since there's only a single English paragraph in the pamphlet. But the site itself is very interesting. Your first stop once you descend the staircase into the underground is the apse of a prior church (1st photo below). Along the route through the underground you'll see several sarcophaguses, a few superb frescoes, and an altar, although everything is a bit confusing due to the lack of signs. Sights from the underground area are shown below.

    

The apse in the underground of San Crisogono
See all San Crisogono photos.

    

A fresco in the underground of San Crisogono
See all San Crisogono photos.

    

2nd century marble sarcophagus with marine decoration, in the underground of San Crisogono
See all San Crisogono photos.

    

Altar built with marble, with frescoes on the outside surface, in the underground of San Crisogono
See all San Crisogono photos.

    

A fresco in the underground of San Crisogono
See all San Crisogono photos.

• My San Crisogono photos