Heidelberg is the most photographed subject in Germany and is still usually shot wrong. The Philosophenweg on the north side is the place from which the castle, the old bridge and the old town line up on one axis; it climbs steeply, takes twenty minutes on foot, and faces south. Which means backlight in the morning and the whole slope in warm light in the afternoon and evening. Walk up early and you get haze and silhouettes.
The second subject is the crowd. Heidelberg has a hundred and sixty thousand residents and some twelve million visitors a year, and they do not spread out. Between ten and five the Hauptstraße is a column of pedestrians and the old bridge is occupied for group photographs by the minute. A session here either starts at seven or it starts at six in the evening, and in between you go down to the Neckar or into the castle gardens, where people disperse.