A secret tip that I recommend to anyone who is in Heidelberg in spring, is the visit of Schwetzingen palace and its gardens. Here, every year Japanese cherry trees are blossoming in front of the Mosque which is a wonderful natural spectacle. After a cold winter there is nothing better than having a picnic with some friends enjoying the first warm sunrays. The garden is of course also a must-see in summer when flowers in many different colours are blossoming. For athletes it is worth to go by bike from Heidelberg to Schwetzingen. There are great cycling trails that lead through a beautiful landscape.