The Hauptstrasse runs for about 1.6km through the heart of the Altstadt from Bismarckplatz in the west to the Marktplatz in the east, and is one of the longest pedestrian zones in Germany. Along its length and in the lanes running off it — particularly Steingasse, Ingrimstrasse, and the parallel Untere Strasse — is the densest concentration of restaurants in the city, covering everything from Swabian and Palatinate cooking to Vietnamese, Italian, and Turkish.
For traditional German food, look for Gasthäuser in the side streets rather than directly on the Hauptstrasse itself: the further from the main drag, the more likely you are to find a place where locals actually eat. Schnitzelbank on Bauamtsgasse is a long-standing favourite for hearty Baden cooking. The Marktplatz itself has several cafés with terrace seating and a view of the Church of the Holy Spirit and the fountain — pleasant for a long lunch if you can get a table.
The side streets around the university buildings on the western end of the Hauptstrasse — particularly around Grabengasse and Friedrich-Ebert-Anlage — have a higher proportion of student-oriented restaurants: cheaper, less formal, and often better value. The Mensa (university canteen) on the Marstallhof is theoretically open to the public and is extremely cheap, if basic.