I believe the Vatican itself to be a work of art that houses a monumental art collection.
The Vatican traces back to the 5th century.
Interesting Vatican City Facts:
The Vatican City is the smallest country in the world with the smallest population. It measures 44 hectares ( 110 acres) and has a population of about 1000 people.
The Vatican has its own Post office and issues its own stamps. The Vatican mail system is widely used by Romans as in most cases is a lot quicker than Italian mail.
The Vatican's railway Station was opened in 1930 and is mostly used for freight.
Piazza di San Pietro (St Peter's Square) and the colonnade were designed and built by Bernini (completed in 1667). At 314 meters long and 240 meters wide it is the largest square in Rome. Bernini (with the help of his pupils) designed the 140 statues of saints which decorate the colonnade.
The Vatican City issues its own passports; the Pope, cardinals, members of the Swiss guard and clergy being the recipients.
The Vatican City is a UNESCO World Heritage Site; the only site to encompass a whole country.
Italians are allowed to donate 8% of their yearly taxes to the Vatican (this is instead of paying it to the Italian Government).
In 2007 the Vatican opted to become the first Carbon neutral state by offsetting their carbon footprint with the creation of a forest in Hungary.
The Vatican stamps its own coins. The €1 coin which has a portrait of the present Pope is in high demand with collectors.
The Vatican museums are over 9 miles (14,5 kilometers) long, and it is said that if you spent only 1 minute admiring each painting it would take you 4 years to complete the circuit!