From the Super Mario Wiki
The Sistine Chapel (Latin: Sacellum Sixtinum; Italian: Cappella Sistina) is a famous chapel located in Vatican City. It is one of three landmarks in Rome Luigi has to visit in Mario is Missing!. The Sistine Chapel is well-known for its ceiling, a huge painting by Italian painter Michelangelo Buonarroti. During the events of the game, the ceiling is stolen by Koopa Troopas, and the chapel is closed until Luigi returns it, for which he is rewarded $900. From the Roman police officer, the player learns that "the Pope went through the roof" when the ceiling turned out missing. In the PC version, however, the Koopas instead steal Michelangelo's Paintbrush. In either case, Luigi must prove that the item in his possession is genuine by answering some of the following questions:
In 1508 Pope Julius II commissioned the artist, Michelangelo, to decorate the ceiling of the Sistine Chapel in the Vatican. He wasn't used to painting on plaster. It took Michelangelo over 4 years to finish painting the 10,000-square-foot ceiling. Much of the painting had to be done in an uncomfortable position. The artist was either lying on wooden scaffolds, or looking straight up. The Chapel's ceiling is breathtakingly beautiful. It is considered Michelangelo's masterpiece.