Osnabrück is easy to reach.
 
The city is a major stop on train lines running between Berlin-Amsterdam and Cologne-Hamburg.

The closest airports are Münster/Osnabrück, Bremen, Hanover, Hamburg, Düsseldorf, Cologne, and Frankfurt (am Main).

There is a shuttle service from Münster/Osnabrück Airport to Osnabrück. The trip costs 9 Euro one way. You can find the schedules here.

Trains from Hanover, Bremen, Hamburg, Düsseldorf, and Cologne stop regularly in Osnabrück. However, you first have to get from the airport to the train station (via streetcar, taxi, etc.). Please ask the airport information center for the best, most affordable way.
Frankfurt airport has its own long-distance train station.

By car, you can get to Osnabrück from north and south via the A 1, from Amsterdam and Berlin on the A 30, and from Bielefeld on the A 33.

The directions to the University of Osnabrück can be found on the site plan (“Anfahrtsskizze”).