Concierge.com's insider take:
Ineffably picturesque, Trastevere is a district of two halves. West of Viale Trastevere, besotted tourists mingle with the few locals who have survived the influx of foreign residents, through twisting alleys packed with bars and restaurants (which are not always the cheapest or the best, but which usually guarantee atmosphere). Every alley seems to lead eventually to Piazza Santa Maria in Trastevere, where the facade of the eponymous church glows with 13th-century mosaics, as does the apse, where the scenes from the life of the Virgin are by Pietro Cavallini, a lesser-known Roman contemporary of Giotto. More of Cavallini's extraordinary work can be seen to the east of Viale Trastevere in the church of Santa Cecilia in Trastevere, where a fragment survives of his Last Judgment—an extravaganza of exquisitely colored angels' wings (2 Piazza Santa Cecilia; 39-06-589-9289; open Tues.–Thurs. 10 am–noon, Sun 11:30 am–noon). This side of Viale Trastevere is altogether a quieter, more laid-back neighborhood.