From the World Heritage inscription:
The Vatican City, one of the most sacred places in Christendom, attests to a great history and a formidable spiritual venture. A unique collection of artistic and architectural masterpieces lie within the boundaries of this small state. At its centre is St Peter’s Basilica, with its double colonnade and a circular piazza in front and bordered by palaces and gardens. The basilica, erected over the tomb of St Peter the Apostle, is the largest religious building in the world, the fruit of the combined genius of Bramante, Raphael, Michelangelo, Bernini and Maderna.
Vatican City is the only country in the world where the area of its world heritage sites is greater than the size of the country (it has locations in Rome which it controls). The photo above is of St. Peter’s Square taken from atop the dome of St. Peter’s Basilica.
View my complete list of UNESCO World Heritage sites.