St. Peter's Basilica is another one of those must see sites when you visit Rome. Allegedly the burial site of St. Peter, the founder of the Roman Catholic Church, the site has had extreme religious importance to Christians for almost 2000 years. At first the burial site of St. Peter was marked with a rock painted red, then a basilica was erected during the time of the first Christian emporer, Constantine. This stood until the renaissance and it was rebuilt, using funds provided from granting indulgences, initiating Martin Luther's 95 theses and the protestant reformation.
The renaissance style basilica is huge, and still reigns tied with a basilica in Brazil as the largest church in the world.
As a bright-eyed, unenlightened, fresh 15 year-old from the new world, when I saw St. Peter's Basilica 15 years ago I was in awe. It was something out of Tolkien's books; the endless caverns of the failed Dwarfen kingdom of Moria. Now when I saw it, it was a really long line to see what was really just another massive cathedral:
The oculus is quite impressive however: