Here are several videos that you can use to help your students understand the basics of Vatican City, as well as the immensity of the Vatican archives. I use these in my Cultural Geography class to intro Vatican City.
This first video is longer than the others and gives a basic summary of what the Vatican is and how it runs. The narrator is a tad bit monotone, but the video is a wealth of information and visual beauty.
This next video is a sneak peak into the Vatican archives, including a love letter from Henry VIII to Anne Boleyn!
This video highlights specific important items in the Vatican archives.