This time's route:
- Brno, Czech - bus (student agency) or train - Prague, Czech: 2 hours 40 mins (same time for bus and train)
- Prague, Czech - bus (Flixbus) - (Germany, Frankfurt - bus (Flixbus) -) Germany, Heidelberg: 7 hours or 8 hours 30 mins
Total: 10 or 11 hours! Too far by bus! But it was worth to go.
I recommend Heidelberg if you want to enjoy seeing old Germany building. It's compact sophisticated clean city. I assume this city has good strategy to run the city. For public transportation in Heidelberg. Remember main Heidelberg train station and Bismarckplatz tram/bus station.
Bismarckplatz tram and bus station. This station is a key to go around the Heidelberg.
Universitätsplatz bus station. This place is also key to go near castle or main street.