It is better not to go on holidays and vacations. There are a lot of people, and the whole vibe is spoiling.
As it is, the place is cool: you can take a look, you can take cool photos, and it's really good to go for a walk. Recommend.
If you find yourself in Heidelberg, then you definitely need to get to the castle. And you definitely need to take a walk, the most interesting things are the courtyards, views, park, etc. Especially in autumn. And the pharmacy museum is good!
Beautiful! Gorgeous view of the city from above. Definitely visit if you get the chance! And climb to the top in an old trailer. I recommend walking part of the way.