I lived in Italy for a year but never managed to find the city's "underground". The best place I found was the Hangar at Via in Selci, 69 near Piazza Santa Maria Maggiore, southwest from the train station (Termini). It is owned by an American from Minnesota (IIRC) and offers several bars and even a smallish dark room (surprisingly lots of action but nothing compared to Amsterdam). You need an UNO Club Card to enter and can buy it at the door (annual subscription or per entry). They are closed on Tuesdays - opens late, no use turning up too early, but if you do and they are already open, there are even a few free internet terminals from which you could surf FT!