This evening is the Long Night of Museums, which is always a great time to be out mingling in the city center. Many of the unexpected museums modernize their image with the use of lights and music to draw in thousands of visitors. Not only are museums open until 2am, but several tour companies offer walking tours around the city. There are also historical tram rides, auto rides, and plenty of glühwein to ease people into the colder temperatures.
For being a relatively small city Munich sure knows how to do cultural events.
One of my favorites is the view from the top of the Deutsches Museum. Unfortunately it's rarely open, because only one volunteer gives tours.