Topped by the highest dome in Rome (designed by Maderno) after St. Peter's, this huge and imposing 17th-century church is remarkably balanced in design. Fortunately, its facade, which had been turned a sooty gray from pollution, has been cleaned to a near-sparkling white. Use the handy mirror that's provided to examine the early-17th-century frescoes by Domenichino in the choir vault and those by Lanfranco in the dome. One of the earliest ceilings done in full Baroque style, its upward vortex was influenced by Correggio's dome in Parma, of which Lanfranco was also a citizen. (Bring a few coins to light the paintings, which can be very dim.) The three massive paintings of Saint Andrew's martyrdom are by Maria Preti (1650–51). Richly marbled and decorated chapels flank the nave, and in such a space, Puccini set the first act of Tosca.