Nelson is small enough to walk almost everywhere in the downtown core. Baker Street is flat; the residential neighbourhoods above it climb steeply up the hillside, which makes walking uphill a workout.
On foot is the default. The distance from Lakeside Park at the west end of town to the east end of Baker Street is about two kilometres — thirty minutes at a relaxed pace.
By car you'll need one if you want to reach Whitewater Ski Resort (20 minutes south), the Kootenay Lake ferry terminal at Balfour (40 minutes east), or any of the trails in the surrounding mountains. Street parking downtown is metered but not expensive; free parking is available one block off Baker Street.
By bike, Nelson has a growing network of cycling infrastructure and the terrain in town is manageable — flat along the lake, with an obvious hill climb if you head inland. The rail trail south of town is good for road bikes and hybrids.
Nelson Transit runs local bus routes, but frequency is low. It is more useful for getting between residential neighbourhoods and downtown than for tourist purposes.