I love the Baroque church of San Carlo alle Quattro Fontane, by Francesco Borromini, which is located next to the fountain ensemble of the same name: Quattro Fontane.  I always try to make a drive by visit to this lovely, calm interior on any trip to Rome.  Here is evidence of my last drive by (walk by, in fact).

The church was designed by the architect Francesco Borromini and it was his first independent commission. It is an iconic masterpiece of Baroque architecture, built as part of a complex of monastic buildings on the Quirinal Hill for the Spanish Trinitarians, an order dedicated to the freeing of Christian slaves.

Borromini received the commission in 1634, under the patronage of Cardinal Francesco Barberini, whose palace was across the road. However, this financial backing did not last and subsequently the building project suffered various financial difficulties.

It is one of at least three churches in Rome dedicated to San Carlo, including San Carlo ai Catinari and San Carlo al Corso.