The most convenient method of transport in and around Oldenburg is the bicycle. There are many shops where bicycles can be rented although the fees can be quite high.
The infrastructure is very cyclist-friendly with numerous paths designated for bicycles around the city centre. It's worth remembering, however, that most of the city centre is pedestrianised. Bicycles are 'verboten' (prohibited) in these areas so remember to leave your bicycle in the surrounding streets and walk to the main shopping streets.
Oldenburg is well connected to main train routes via Bremen to the east and Emden to the west. When arriving by train, don't miss having a look at the train station building. Built in 1911-1914 shortly before World War I, it shows a modern construction and art nouveau ornaments.
Unfortunately the brick ornaments in the main hall have been painted over. Only the station restaurant, the former first class waiting room, still shows original ornamental murals.
The easiest way of getting around is by bicycle. Oldenburg is small enough that most of the things can be reached by bike and it eliminates the hassle of finding a parking spot. Especially since the pedestrian zone is closed for cars. Since most of the people living in Oldenburg are using a bicycle, the car drivers are also trained to pay attention to bicyclists.