If I had only one day to explore Rome-Suggestion please :D?

Question

I know that there are so many things to see and do in Rome that it is immeasurable.... but if I had only one day to explore Rome, what would you say are places or things that I must see or do, besides the obvious Trevi Fountain, Vatican City, Pantheon, The Roman Forum, Borghese Gardens, etc, etc.
Give me something that not many people know about or something that you deem as something that has to be seen or experienced.
I welcome anything from answers to my question to tips and advice about my visit to Rome from anyone and everyone!

And, for you world travelers out there.... feel free to leave me all the tips, stories, and advice you can write! This is for my first trip to Rome and I have wanted to go since before I can even remember. So, I appreciate all of your responses.
Oh, and I am a young girl, 20, so any tips on safety would be great too.

Thanks and I can't wait to hear all of your responses! : D

P.S. I have extensively studied Italy, as it has been a goal of mine to get there practically my entire life. I know about the gypsies and pickpockets, and most of the popular sites and stuff, I even applied to the American University of Rome.
I am not going to be spending only one day there but I thought that saying this might highlight the fact that I want to hear about must sees that are not very well known. Oooo, and I would love to hear your stories about your experiences in Rome.

Answer 1

The catacombs at the Appian Way.

Answer 2

You've pretty much listed down the must-see sights and it will take you the whole day to go through them and even more time to appreciate them.

You can try having gelato at the Spanish Steps or Piazza Navona for a break. Eat the pizza, take lots of pictures and watch your back. Lots of pickpockets in Rome and if you look and act like a tourist, you're a prime target. Enjoy Roma!

Answer 3

The Sistine Chapel is the most amazing thing!!!!! That's the one you have to go even if you have an hour!!!!!!