In the week after Easter I did a hiking trip around the Edersee, a reservoir lake in the area of Kassel. The forest around it, the “Kellerwald”, is a UNESCO world cultural heritage, because it is mostly untouched and slowly becomes a type of jungle. So it really is a nice place to hike. … well, in theory, at least. I guess as soon as the leafs are green and the temperatures are warm it is a fantastic place to be. Unfortunately, this both was not the case at the time I was there.
As you can see, big parts of the lake still were frozen and there was a lot of snow everywhere. On the other hand, I did met only very few people during this three day trip. In essence I can only recommend this area, but I you should decide to go there, wait until it is warmer (like right now, for example).