Bielefeld University in Google Maps
Bielefeld is easy to reach (see below) both by car and by train: every hour an intercity train on the route from Cologne/Bonn to Berlin stops at Bielefeld Hbf. Then you take "Stadtbahnlinie 4" with direction "Lohmannshof" till "Universität" (7 minutes).
Plan of Bielefeld "Stadtbahn-Netz" (in German)
From the north: You can take the A2 from Hannover to Dortmund, exit at "Bielefeld-Zentrum", follow the street signs towards the centre ("Zentrum"), and from there the University ("Universität") is signposted.
From the south: You can take the A2 from Dortmund to Hannover. At "Dreieck Bielefeld" on the A33 towards "Bielefeld-Zentrum", exit "Bielefeld-Zentrum", towards Zentrum on the B61, exit "Universität", way over Stapenhorststr., Kurt-Schumacher-Str. (is signposted).