To clear up any confusion we first need to define some terminology:
Vatican City is a city-state with clearly defined borders. It is an independent country surrounded by Italy, and presided over by the Holy See (the Catholic church’s jurisdiction), with its own leader (the Pope), currency (Vatican-issued euro), security forces (the Swiss Guards), post office, etc.
Vatican Museums & Sistine Chapel
Inside the walled borders of Vatican City are the Vatican Museums. These museums are vast and contain huge collections of art and stunning antiquities, and the world-famous Sistine Chapel. They make up a large part – but not all – of the Vatican buildings.
Inside the Walls: Vatican Gardens & Auditorium
The rest of the space within the Vatican’s city walls is made up of chapels, ceremonial spaces, offices, accommodation, the papal apartments, the Vatican gardens, restaurants, a bank, shops, an auditorium (in which Papal audiences take place), and even a radio station. These are not generally open to the public, though it is possible to go on a guided tour of the gardens.
Outside the Walls: St. Peter’s Basilica & Square
However there is also a small part of the Vatican City that is outside the walls and may be wandered into from the street. In this space is St. Peter’s Square (Piazza San Pietro) and St. Peter’s Basilica (Basilica di San Pietro) which is the world’s largest church.
When someone asks “are you going to visit the Vatican while you’re in Rome?” they likely mean the Vatican Museums. The Vatican Museums require you to book a guided tour or buy an entrance ticket and take about four hours to go through, even to scratch the surface of the 8 miles of corridors, and to visit the Sistine Chapel. (Note that if you opt for a guided tour, you usually get a skip-the-line visit to St. Peter’s Basilica via the papal corridor direct from the Sistine Chapel, meaning you don’t have to line up twice.)
Confusingly though, they might sometimes mean St. Peter’s Basilica. Unlike the museums, Michelangelo’s stunning St. Peter’s Basilica is free to visit. The largest church ever built (it is not a cathedral!) has a different entrance to the Vatican Museums, about half a mile away round the city walls – you line up in St Peter’s Square to go through security check and enter the church through the front door. Please note that for any gender, shoulders and knees must be covered to be allowed entrance to the Basilica. During warm months people can and do get turned away regularly at the door for not covering themselves up, even after waiting in line for half an hour. If in doubt, carry a pashmina or sarong to throw over yourself when at the clothing check.
You can usually visit the Basilica in the space of just over 90 minutes, including waiting time (depending on how long the line is, which can seem ridiculously long, but usually moves quite quickly). However if you’re in a hurry, you can also skip the lines at St Peter’s.
Pro tip: skip the line at St Peter’s Basilica
Even though it’s free, during high season (spring and summer months) the line for the Basilica can be 30-45 minutes long, as crowds are limited and you have to go through a security check. By subscribing to an audio guide service you can skip these too: Book an audio guide and skip the lines at St Peter’s for only €19.50 >
Finally note that since the Basilica is a working church, it is sometimes off limits to visitors; if you’re lucky though you may even see the Pope giving mass, or even giving the Papal Address to the crowds in St Peter’s Square – usually at 12 noon on Sundays.