We've spent about 6 days in Rome and I'd like to have another week to
see the things we missed. Of course how long you spend depends on
your stamina for walking and how soon you start missing the sights and
tastes of home.
The Vatican Museum is separate from St. Peter's Square/Basilica and
could take a whole day in itself to appreciate. The Vatican Museum,
by the way, has a cafeteria halfway through, which was the only place
we could find fresh fruits & vegetables in Rome. There are probably
produce markets somewhere in town, but we didn't come across them.
You mentioned the Forum, but you can't miss the Colliseum. If you
liked St.
Peter's Basilica, check out "San Giovanni en Laterano", the smaller
"backup version" of the church. And next door to that is the Santa
Scala (Holy Staircase) which is said to be the stairs Jesus walked up
to trial. Constantine's mom brought them back from the Holy Land and
visitors walk up the steps on their knees to have their prayers
answered. (Painful!)
Their are catacombs on the edge of the city and a cool excavation of
an ancient christian church underneath the church of San
Clemente...and under THAT is another recent excavation of a
pre-christian cult temple!
If you've seen the film "Roman Holiday", you'll want to stick your
hand in the mouth of the "Boca di Verite" (several minutes walk west
of the Capitol, I believe)
http://www.athanasius.com/rome/boca.htm
and visit the square in front of the Pantheon, and of course throw a
coin in the Trevi Fountain (especially when lit up at night!)
http://www.davidnemeth.com/trevi.htm
Then there's the museums....
Having said all that, Rome is an extremely busy city (watch out for
pickpockets) and it is a really nice break if you can take two days to
go to Assisi and experience the peaceful countryside of St. Francis.
Have a great time! And read books & watch videos about Rome as much
as you can before you go! You'll get ten times more out of your trip!
P.S. Get into St. Peter's as early as possible (especially to go to
the top of the dome) or you'll waste LOTS of time standing in line.
Oh yeah...look for guides offering free tours in front of the sites.
They are legit. Some do it hoping you'll sign up to pay for other
tours they offer, but there's no obligation.