Heidelberg on Neckar river is set among lovely hills, where the Neckar valley opens into the Rhine valley. Its famous 600-year-old University of Heidelberg (the oldest in Germany, founded in 1386) has several Renaissance towers and turrets at the base of a hill near Heidelberg Castle. Be warned: It is a draw for fleets of tour buses in the summer.
The best way to enjoy the town is to stroll along the Hauptstrae in the old section to mingle with the local crowds and to sit at one of the many street cafes or beer halls.
Also visit the Heidelberg Castle which changes colors with the different angles of the sun. View the city from the Karl-Theodor Bridge which citizens of Heidelberg just call Alte Brucke (Old Bridge). The nearby Philosophenweg gives a great overlook of the city, it is definetly worth walking up this steep path.