While Vatican City is a separate country, no passport is necessary -- you can just walk right in.  Visitors to Vatican City enter through the magnificent St. Peter’s Square, with the beautiful round colonnade by Gian Lorenzo Bernini.  For all sorts of transportation maps providing more than adequate visual explanation of how to get to and from this country, the smallest in the world, check the official site’s offerings .

Coming and going from Rome’s runways are relatively easy endeavors, though if you visit in high season (roughly Easter through early fall) you should expect lots of fellow tourist congestion.  Airline ticket prices will also be more expensive for visits during this time of year.  Flight times from New York to Rome are only eight hours, ten from Chicago, and about twelve from Los Angeles.

Rome is a small enough city that you may wish to just walk from attraction to attraction to the Vatican, though the heavy foot traffic can make for some aggravation.  The Metro makes for easy getting around (closest stops are Ottaviano/San Pietro and Cipro/Musei Vaticani), as do buses and trams, which can take you to just about anywhere in Rome, including the Colosseum and the Vatican. 

If you wish to move about the city by cab, call for one or find the nearest taxi stand, as hailing can sometimes prove rather difficult, and when in Rome do not always do as the Romans do; instead, why not avoid brutal rush hour traffic (which includes an afternoon lunch rest-up).