Downtown Pittsfield is walkable, especially around North Street, Park Square, the theatres, and the Berkshire Museum. The lakes, Arrowhead, and Hancock Shaker Village are spread farther out, so a car or bike makes the city far more useful as a base.
Local buses cover some routes, but they are not designed around sightseeing. In winter, watch road conditions in the hills; in leaf season, expect slow scenic traffic rather than city congestion.