Damn short notice, Zagreb-Munich bus is cheap, but 7 hours ride still...if you said earlyer, like, a month
But yeah, BenJs suggestion is by far the best if you can make it to Montreux.
If you have only one day, enjoy Munchen, be sure to visit Euro-Skate hall, I heard it's nice, tho, you'll freeze to death if you'll ride the outdoor street section...