San Francisco, you say...? Lunch at Alice's Restaurant on Skyline Boulevard is usually a must for me, whenever I'm in the Bay Area.
http://www.alicesrestaurant.com
Then head South and get onto Empire Grade and Bonny Doon down to Davenport on Hwy 1. Take in Stage Road somewhere along the way. If you like goat tracks look for the roads named "Grades" - China Grade, Ice Cream Grade et al and if you like a real challenge try Tunitas Creek Road down from Skyline Blvd to the Pacific Ocean at Half Moon Bay.
Other than that, there's not much to do....
Ok then, a couple of mountain rides. Cross the Golden Gate into Marin and ride up Mt Tamalpais, come down and ride Hwy1 up to The Sand Dollar Restaurant at Stinson Beach for lunch. Ride up Mt Hamilton, outside San Jose. Visit the Lick Observatory. Ride down the other side and do Mines Road and Del Puerto Canyon Road. There's more and more. The Bay Area is criss crossed with great riding roads and attractions.
Further away the Sierra Mountain passes such as Sonora Pass and Monitor Pass offer stunning riding roads.
Much depends on how long you're there for and if you have other further away desinations in mind, e.g. Yosemite, Death Valley, Lake Tahoe. Are your renting a bike, if so from which company? If by any chance it's from Dubbelju, I know they'll be more than happy to make good suggestions as I'm sure will the staff at other rental companies.
Have a great time.