The Burgwaldpfad (translates to "castle-forest-trail") is a roughly 50k long trail that connects the towns of Frankenberg in the north and Marburg at the southern end. It's a well marked hiking trail, mainly on forrest roads, that leads through the name giving Burgwald. This is the landscape the famous brothers Grimm had as inspiration for their fairy tales when they lived in Marburg at the beginning of the 19th century: Dark and silent forests, mixed up with rural cultural landscape. Scattered in between little villages, creeks, rivers and castles (most of them just ruins today). All in all it's a nice and enjoyable route that's really representative of the surrounding landscape.
Photos: From the corresponding Wikipedia-articles of Christenberg, Meltau, Elisbathekirche