Duluth is a hilly city built on a steep slope above the lake, which makes walking between the upper hillside neighbourhoods and the waterfront more strenuous than it looks on a map. Canal Park and the lakefront are flat and entirely walkable; downtown is manageable on foot.
The Duluth Transit Authority runs buses connecting most parts of the city. Service is adequate for getting from downtown to attractions like Glensheen and Fitger's, though frequency is limited by Twin Cities standards.
A car is useful if you plan to explore the North Shore — Highway 61 northeast of town passes through state parks, waterfalls, and small towns that are difficult to reach without one. The Lakewalk cycling and pedestrian path along the waterfront is the pleasantest surface-level route in the city.