Location
Regensburg is located in Bavaria, in southeastern Germany, not far from the borders with the Czech Republic and Austria. Nuremberg lies to the north and Munich to the south. 

Travel by plane
It is also in Nuremberg and Munich that you'll find the nearest international airports. By road it's just an hour from Munich Airport to the Jahnstadion (practically Autobahn all the way), while from Nuremberg Airport it also takes about an hour (Google say 1 hour 8 minutes) and is also Autobahn nearly all the way. By rail there are direct regional trains from Munich Aiport to Regensburg Hbf (main station) that take around 1 hour 20 minutes, while from Nuremberg Aiport you'd take the U2 underground to Nuremberg Hbf and then potentially an ICE express train from there to Regensburg (total journey time c. 1 hour 5 minutes).

Travel by car
Regensburg is served by two motorways, the A3 and A93, which cross just outside the city. The A3 runs diagonally across the whole of Germany, from the Dutch border in the northwest to the Austrian border in the southeast. Cities along the route include, for instance, Cologne, Frankfurt and Nuremberg. The A93 meanwhile runs north-south from the northern border of Bavaria down to south of Ingolstadt.

Both of those motorways are, of course, linked to the rest of the nationwide Autobahn network, enabling driving times from other German cities to Regensburg of, for example, approximately those shown here:

Cologne: 5 hr 10 min
Dortmund: 5 hr 50 min
Frankfurt: 3 hr 25 min
Berlin: 5 hr 10 min

If you're thinking of hiring a car, I'd try Avis, Budget or Europcar.

Travel by coach
FlixBus, Germany's leading long-distance coach travel company, run services from just outside Regensburg Hbf (main station). For travel times and fares (which can be very cheap) check out the FlixBus website.