The old town is easily walkable — the main sights sit within a roughly 1 km radius of the Stadtmarkt. The Herzog August Bibliothek, the castle, the Marienkirche, and the Little Venice canal district are all on foot. There is no tram or metro; local buses cover the wider town but are unnecessary for sightseeing.
Cycling is a pleasant way to explore the flat terrain and the paths along the Oker. The town is well set up for bikes, and cycling is a legitimate option for day-trippers arriving by train from Braunschweig if you bring your own.
For the JägerMeister production site and visitor experience, which sits on the edge of town, a short taxi ride or bus trip is more practical than walking from the centre.