With such a short amount of time in town, and considering you're arriving somewhat late in the day, I'd suggest a bike tour. I recommend Mike's, who pick up at the Marienplatz at 4:30pm, and take you on a 4 hour tour that includes a stop for dinner and beer in the English Garden. As ritesa mentioned, the sun sets late in June, so you may as well enjoy the extended daylight and cover some ground.