Rome's only public toilet to remain open is in Piazza Vittorio.

Rome has 57 public toilets, located underground and at street level, however all but one of these is now closed according to a report in Italian daily newspaper La Repubblica.
Despite the millions of tourists, residents and homeless people in Rome, the city's only public toilet currently operational is in Piazza Vittorio not far from the capital's main railway station. Rome's last public toilet to remain open is maintained thanks to a collaboration between the local municipal council, the capital's refuse and sanitary authority AMA Roma, and a residents' committee. The findings are the result of a report by Carteinregola, a non-political association whose volunteers deal with various issues affecting the public in Rome including mobility, heritage, public services and the environment. Carteinregola says that the capital has witnessed the "progressive closure" of public toilets over the last decade.
La Repubblica reports that in 2011 the annual cost to maintain Rome's 57 public toilets - entrusted to AMA Roma - amounted to almost €1.5 million. The city paid for the renovation of a number of these toilets in 2013 and again in 2015, when eight public toilets in the centre were upgraded in preparation for the Vatican's Holy Jubilee Year of Mercy. 
However the newly-restored toilets were shut on 21 November 2016 by the city's then commissioner Francesco Paolo Tronca, the day after the Vatican's jubilee year ended.
In contrast to Rome's poor public sanitary facilities, the Vatican has excellent public toilets under the colonnade in St Peter's Square, which even includes showers for the homeless. 
The millions of tourists who come to Rome each year must rely on the goodwill of the city's bar owners who are required by law to have a functioning bathroom.