The Altstadt — the old city — is the area within the line of the long-vanished medieval walls, now traced by a ring road. It is small enough to walk across in fifteen minutes and most of it is closed to traffic. Cobbled lanes, half-timbered houses, three squares, two surviving gate towers, the cathedral, and the famous Bächle running everywhere along the streets.
Despite heavy Allied bombing in November 1944, the medieval street pattern survived because the post-war reconstruction deliberately respected it. Most of what you see today is reconstructed rather than original, but it is done well enough that the city still feels properly old. The most evocative quarter is the Insel ("island") in the southeast, between the Schwabentor and the canal that runs along Gerberau.