Vatican might be the smallest country in the world, but it surely has a lot to see. Despite its overwhelming gloriousity and grandiosity it is possible to see all the main sights in one day. However, there are some things you should be aware of.
1. Get ready to queue
As Vatican is one of the most visited religious sights in the world, there are a lots of tourists and pilgrims visiting Vatican around a year. If you don't want to spend half of the day queueing make sure you visit Vatican either in spring or autumn time. The busiest season is from June to August, not forgetting the Easter. In the busiest times you might end up queueing for several hours, which definitely isn't fun under the ruthless Mediterranean sun in mid-summer. The temperatures can rise up to 40 celsius.
However, if you decide to go during summer time, with extra payment you can skip the lines while booking online from Online Ticket Office of the Vatican Museums.
2. Do your research
Vatican indeed is a tiny country, but the amount of things to see is surprisingly broad! If you absolutely want to see absolutely everything, one day won't be enough. I recommend to do some research before the visit and maybe mark down some things you really want to see. I was overall interested in Vatican and I didn't have any must-sees except the Creation of Adam which is probably the most famous piece of art by Michelangelo located inSistine Chapel. So I ended up just wandering around and that was one way to see things there.
Sistine Chapel is located in the heart of Vatican Museum and it takes time to actually walk all the way there. It's full of people taking pictures despite the signs forbidding it. There are several workers trying to hush people down without success. I need to admit that the whole ceiling was beautiful but after hours of seeing glorious art I was in a way starting to get fed up with all of it.
3. Ethnological Museum
After hours of wandering through the halls of the St. Peters church and the museum I discovered something slightly different. There is an Ethnological Museum full of beautiful ancient objects from different cultures collected from all over the world. I had no idea that there was so interesting things there. As a culture and history geek (and not that artsy), I was happy to discover this part of the museum.
4. Meet The Pope
If you are eager to see the Pope you should visit Vatican on Wednesday (when the Pope is in Vatican) for Papal Audience. During Papal Audience the Pope gives speeches and do readings mostly in Italian but also in other languages such as English, Spanish and German. There are a lot of people attending this event so it is good to arrive early to get a good seat. In order to attend to this event you need to have a ticket which you can pick up from St Peter's Square a day before the event.
5. Be respectful
The Vatican city is the center of Catholic world and very holy place for hundreds of million Christians around the world. Therefore visitors should behave respectfully. Remember to cover your shoulders and knees when entering Vatican. In the church there are few sections that are only meant for prayers, so read the signs carefully.
6.Need a guide?
If you don't have knowledge of the art history and you would like to learn something about the pieces and buildings there, guide is recommended. There are plenty of eager guides trying to sell you their tours just outside the Vatican. However you should pay attention to their prices as there are plenty trying to get away with way too pricy tours and so little knowledge. I recommend either renting an audio device which you can carry around and choose what you want to hear. If you know a local who would be eager to join you, that's always a good idea.