Phanteon

Commissioned by Marcus Agrippa, restored by Domitian, and subsequently rebuilt by Hadrian (who added the dome) before being turned into a church in the early 7th century by Pope Boniface IV. The building's sole source of light is the opening at the dome's apex (the oculus); according to popular legend, this formed the base for the bronze pinecone that is now in the Vatican's 'Pigna' courtyard, where it is used as a fountain. Many famous Italians are buried in the Pantheon, including Renaissance painter Raphael and King Vittorio Emanuele I. A must  if you are in Rome, you can't miss this marvelous spectacle.