A 5th-century basilica near the Colosseum, housing two things worth seeing: the chains (vincoli) said to have bound St. Peter in Jerusalem, displayed in a reliquary under the high altar, and Michelangelo's Moses. The seated Moses — part of the never-completed tomb of Pope Julius II — is one of Michelangelo's most powerful sculptures. The horns on Moses's head are a medieval mistranslation of the Hebrew word for "rays of light."
Tucked down a side street and easily missed, which means it's often quiet. Five minutes' walk from the Colosseum.