Like you, every year about 10 million tourists pass through the miles of corridors in the Vatican Museums to go straight to the Sistine Chapel, where they are enchanted, or rather overwhelmed, by the beauty and power of Michelangelo's frescoes. But you shouldn't forget that this is firstly a place of worship: for over half a millennium this is where the "conclave" has been held, which is the solemn ceremony for the pope's election, with a ritual that involves and excites the faithful.
Let's start with a bit of history: the chapel is linked to the name of Pope Sixtus IV, who was elected pope in August of 1471. During his long pontificate he left a serious mark on the city's architectural and urban planning, especially on the Vatican hillside next to the ancient Basilica dedicated to St. Peter, which would be completely torn down to build the actual one.
He set up a grand library that was managed by renowned humanists and decorated by Melozzo da Forlì, commissioned Antonio del Pollaiolo to create his impressive bronze burial monument, and above all he had a place built for holding the conclave and other important pontifical ceremonies: this was precisely the Sistine Chapel.
Its exterior appearance is not very striking: it's a simple, rectangular building covered by a sloping roof where you can see the famous chimney that reveals the outcome of the cardinals' vote. The chapel is situated next to an ancient tower wall, and it was not by chance that the works were started in 1477 by an architect who was also an expert in fortifications.
Of course the chapel's interior is completely different, starting with the refined marble mosaic floor and the elegant marble transenna that divides this spacious rectangular hall that's forty meters long and about fourteen meters wide into two separate spaces.
FUN FACT: Michelangelo obviously had assistants, even if just to mix colors and pass them to him. But he hired and fired them quite often, and none of them could claim that they had collaborated on the entire ceiling of the Sistine Chapel.