Vatican City is it's own "country". You must bring your passport to get in and will be required to go through security before entering. It is made up of many museums and gardens, and of course the Sistine Chapel and St. Peter's Basilica. I recommend getting a tour guide, they are easy to find and affordable as they hang out around the Vatican just waiting for their next customer. (If you are military you can get a USO tour guide, they are awesome, contact the office in Rome).
Depending on your tour guide and your preferences there are many different things you can see in the Vatican. We saw the Sistine Chapel ("Creation of Adam" painting on the ceiling, aaaammaazing!), St. Peter's Basilica, animal statues, a hall of statues, beautiful old HUGE tapestry's hung on the wall in a low light hall and we walked through a gallery of what looked like 3D molding on the ceilings and walls but was actually a 2D painting.
|The body that Adam in Michelangelo's "Creation of Adam" in the Sistine chapel (no pictures allowed) is based off of.|
|So much beautiful artwork.|
|One of the Pope's entrances to the Vatican.|
|Swiss guard outside St. Peter's Basilica.|