The hike is split into two parts. The first part starts at the university and takes about 5-6 km before it reaches "Peter auf'm Berge", a restaurant at the crest of Teutoburg Forest where you can stop for cake and coffee or tea. After this, there are two possibilities to proceed:
1) You cross the Teutoburg Forest and descend in southward direction towards the train stop "Quelle" (3-4km). From there, trains to Bielefeld central station ("Hauptbahnhof") depart at xx:12 and xx:40.
2) You proceed eastwards on the hiking path "Hermannsweg" which follows the crest of the Teutoburg forest. After about 6 km, you arrive at the tram stop "Adenauerplatz" which is located right next to Bielefeld's castle, the Sparrenburg. From there, you can either walk up to the Sparrenburg and enjoy the view over the city or you can take the tram number 1 which takes you back to the central station ("Hauptbahnhof").