From SFBC:

Ride through the literary history of San Francisco. Tour neighborhoods as varied as North Beach and the Mission while learning facts, tid-bits, and heresy about the City’s writerly past. Be prepared to meet some authors along the way. Expect a two-hour, fairly easy-going ride (minimal hills!). Eat beforehand, but time permitting (and desired) we will stop in a coffeehouse for refueling.
SF Bicycle Coalition recreational rides are free for SFBC members (a $5 donation from non-members is appreciated); rain cancels rides.