Prague is a good choice, and it’s only about 6 hours from Munich, so that’s doable. Another option would be to head to Salzberg, Austria. It’s not as far as Prague, and also a great place.

Is your entire trip 8 days, or you have 8 days to spend travelling outside of your visit in Munich?

If it’s 8 days total, then you probably only have time to see one other place, but if not, then you could see both Prague and Salzberg.

I agree with Praque as a stop and maybe another choice could be Berlin, Berlin has a good nitelife (if that’s what you are into), plenty of history, the people are more laid back. I found that I walk a lot in Berlin in the 3 times I visited

Fussen and Neuschwanstein Castle was really cool. The train to Fussen takes 2 hours from Munich. Most people go straight to the castle, but the town is really neat too.

Other than that, Salzburg is a really great city to visit.