It's possible to visit Speyer on a day trip between Frankfurt and Heidelberg. We boarded the S-Bahn train in Heidelberg and within an hour were in Speyer. Again, it was about a 15 minute walk from the train station to the old town. Speyer Cathedral anchored one end of the pedestrian shopping street. Even though it was Sunday, many of the shops were actually open, even up to 7-8 pm! This was a total surprise for a German city!
We could see the clock tower anchoring the other end of the shopping strip.
We found a local wine pub tucked away on a back alley and stopped in for a glass of vino.