The city itself is lumpy, very lumpy. It wasn't chosen as the backdrop for a thousand car chases (and adverts with bouncing balls) because it resembles an ironing board. One block of
Lombard Street, for example, is close to 1:3, and the town is marked by the Pacific Heights, Nob Hill etc. But, it is fantastic walking round there and Chinatown isn't too far from there. Ashbury Heights and the Twin Peaks are also pretty steep, but great places to visit.
Obviously, though, the waterfront (Fisherman's Wharf, Embarcadero, Presidio etc) are flat and good cycling, mostly tourist friendly and safe, unlike some of the "Projects" areas further south in the city.
I haven't cycled there but the Golden Gate Bridge would be a magnet for me, as would, having driven it a few times, the
Bay Bridge to Oakland, with the sight of the cranes in Oakland Harbour,
allegedly the inspiration behind the design of the AT-AT walkers in the Empire Strikes Back.