Gruibingen claims to be the first feng-shui motorway caf in Europe. You can see the details--the…read morebottled water is to your left as you walk in, the stairs don't face the front door, and stuff.
Not sure if the feng shui does the trick, or if it just happens to be a nice enough place with a pleasant outdoor terrace, but I find Gruibingen one of the nicer stops on the busy A8.
Stop in and recharge your chi after the aura-bronzing experience that Stuttgart usually dishes out.
Note: Now accessible from both directions!