The Roman Forum: as it is just the last stop on any bus route I take it is my absolute favorite spot. It is set up so you can sit outside and look out on the majority of the hill.
Honestly if you are visiting Rome, trying to keep it cheap and aren’t interested in much history, don’t bother paying the 12 euros. Instead just spend an afternoon outside, grab lunch and go sit by it because it is truly beautiful.
One of my favorite things is just to sit and think about all the people who gathered here everyday. All the processions that occured from the Empire to Mussolini, it is truly facsinating how much history is present in this one spot.