The Imperial Forums occupy the large field of archaeological rubble that lies between the Capitoline hill and the Colosseum. Although almost all of the buildings are entirely ruined, with a little imagination it is still possible to get a lot of pleasure out of a trip to the forum.
If you want to understand what's what, you will need to take a good map or at least eavesdrop on the many tour guides.
Things to See
The curia (which housed the senate) and the house of the Vestal Virgins are among the highlights. There is also the small mound of earth marking the spot where Julius Caesar is supposed to have been cremated. People still regularly leave flowers and, inexplicably, coins on the mound. Nearby is the Palatine hill where there is a great deal more to see although, unlike the forum, the Palatine is not free to visit. The Mamertine prison in the corner of the forum features an dark, deeply unpleasant subterranean cell where St Peter is thought to have been held until his execution. (The exit takes you out past a gift shop.)
Visiting the Forums
The nearest metro station to the forums is Colosseo on Linea B. When you come out, walk straight ahead past the Colosseum and then turn right onto Via Sacra. The forum can also be approached from the far end at the Capitoline hill, which offers an excellent view of the layout.
Entrance to the forums was free for several years, but in 2008 the turnstiles went back up, and since then it has been included on the joint ticket for the Colosseum / Palatine Hill.