About half way between Vienna and Prague is Brno, a fairly large Czech city which was the perfect place to break up the 4 hour drive between the two cities.
I was surprised to see that Brno is a very pretty city with many of the Habsburg era buildings you see in other cities in the region. There is a castle high up on the hill where you find great views of the city including the imposing cathedral as well many ghetto type apartment buildings in the suburbs.
We stayed for lunch and then spent an hour or so walking around. I think it would be worth exploring a bit more if we had the time.