The Cattedrale di San Pietro Apostolo stands on a small square just off the main piazza. The original structure dates to the 13th century, but it was substantially rebuilt after 1596 and the current Baroque facade — attributed to the school of Giacomo della Porta — gives the cathedral its formal character. The interior was severely damaged during Allied bombing in 1943 and heavily restored afterwards; what you see today is largely a post-war reconstruction. Worth a brief visit for the facade and the peaceful square in front of it.
Frascati Cathedral
Baroque cathedral rebuilt after wartime bombing, with a 17th-century facade