Detroit is a driving city — the layout, the distances, and the post-war planning all assume a car. Renting one is the easiest way to see Dearborn (Henry Ford Museum), Bloomfield Hills (Cranbrook), Belle Isle, and the various neighbourhoods. Parking downtown is plentiful and not expensive by big-city standards.
For downtown and Midtown alone, mass transit works. The QLine streetcar runs the length of Woodward Avenue between downtown and New Center, stopping at most of the major attractions. The People Mover is a small elevated loop around the downtown core — useful and pleasingly weird. The DDOT and SMART bus systems cover the city and inner suburbs respectively.
Uber and Lyft both run. Cycling has improved with new lanes along the RiverWalk and the Dequindre Cut, and MoGo bike-share has stations across downtown, Midtown, and a few outlying neighbourhoods.