Rittergasse is the classic Stolberg walk: narrow, sloping, and lined with half-timbered houses that make the town feel older than its modest size. The point is not one single facade, but the run of houses, courtyards, beams, and rooflines between the market and the castle slope.
Give yourself time to wander into the side lanes rather than treating it as a route from one sight to another. Stolberg's main attraction is the old town as a whole.