getting there: metro Linea A/Barberini
open: the church doesn't seem to be open very often
The mid 17th century dome pendentives, the symbols of the Franciscan order, Chastity, Humility, Poverty and Obedience, were by Pietro Paolo Ubaldini.
I found walking around Rome was the best way to see everything but the metro, trams and buses are an easy and cheap option also.
Most buses and metros do get crowded and tickets must be bought before boarding and validated when you first get on but it is a great way to get around and see Rome if you are short on time or suffer from sore feet.
Buses #40 and #64 starts at Termini and ends near St. Peter's traveling past other places of interest, returning the same way.
Bus #75 takes you past the Colosseum
Bus #910 takes you to Villa Borghese
#64 & #40 Express Bus
Corso Vittorio Emanuele II
The Electric buses that are around Rome can travel into the older parts of the city and wind around the narrow streets. Bus #116 travels though the streets of Centro Storico.
B.I.T (Biglietto Integrato a Tempo) is the standard ticket valid for one metro,tram or bus ride for a 100 minute period.
B.I.G ( Biglietto Integrato a Giornaliero) is a daily ticket valid for unlimited metro, tram, bus and train travel within Rome.
B.T.I (Turistic) is a 3 day tourist ticket and the same as B.I.G but for more days of travel.
Purchasing Bus and Metro tickets.
Newsstands, train stations, metro stations, kiosks with the ATAC logo and tabacchi shops sell tickets for trams and buses.
Large fines apply to travelers not holding ticket. Tickets once they are validated, start from the time they have been stamped.