The true social crux of Munich, Marienplatz is a beautiful town square surrounded by the stunning architecture of the Neue Rathaus (the town hall, across the way from its previous incarnation), the massive Frauenkirche (the international symbol of the city), and a number of crowded cafes, bars, and restaurants.
In the middle of the square, you'll find the Mariensäule, a column topped by a statue of the Virgin Mary, after which the square is named. Also, if your timing is right, you can catch the Glockenspiel located in the Neue Rathaus wall periodically performing a short reenactment of the marriage of a local duke to the delight of the spectators. In Munich, there are some definite must-see's. The Marienplatz is unmistakably one of them.