Well saints be praised, literally! The Vatican is still one of the few places left that does not have an admission fee! With the exception of the private museums, you can explore the grounds and the interior free of charge. The two main entrances to Vatican City for tourists are the Vatican Museums, accessible from Viale Vaticano on the North side of the city state and St. Peter's Basilica, on the Southeast side of the city and accessible from Via della Conciliazione. While St. Peter's Basilica is open all day long, the Vatican Museum entrance closes at 3:30PM on weekdays and 12:20PM on Saturdays, so if your plans includes the museums, it behooves you to first visit the museums and then the church.

It's interesting to note that the Vatican is considered to be a separate country with its own postal system, which, by the way, is rumored to be more efficient than most postal systems.