We stayed right around the corner from the Colosseum so we got to see it everyday. It's amazing to see something like that still standing.
We took a tour of the Colosseum which at first was a little disappointing. The guide gave us a very quick bit of info outside, some more quick info inside, and then said we had 10 minutes to look around. 10 minutes!?! Luckily, we figured out how to take the tour of the below the floor area that just opened two weeks ago. That was a great tour!