A still-functioning convent built around a peaceful courtyard garden, Santa Cecilia contains the partial remains of a masterpiece of Roman medieval painting, the “Last Judgment,” by Pietro Cavallini (ca. 1293). Enter to the left of the main doors; a suora (nun) will accompany you upstairs to see it. Inside the airy church, over the altar, is a late-13th-century baldacchino by Arnolfo di Cambio. The church is built on the reputed site of Cecilia’s ancient palace, and for a small fee you can descend under the church to inspect the ruins of Roman houses, as well as peer through a gate at the faux grotto beneath the altar.