We stayed at an air bnb right down the way from the old town. We could see the castle from the window in the hall of the building. Exploring the town center and going ice skating in the rink right below the castle. https://www.tourism-heidelberg.com/explore/historical-sights/schloss-heidelberg/index_eng.
There was a wonderful Irish bar called the Dubliner that had karaoke on Friday nights. There are hotel rooms on the upper floors that we are really wanting to stay in next time.
https://www.booking.com/