I'm not sure what I can possibly say about the Colosseum that hasn't already been said. If you want to take a look inside, be prepared to wait on massive lines! I much prefer the view at night when it's lit up. Right beside the Colosseum is the Arch of Constantine. As an American, I'm not used to being surrounded by ancient ruins so something this grand is truly otherworldly to me.
Italians, they just stroll on by.