Rentals: You can rent bikes near the suggested routes at Park Cyclery, 1865 Haight St., (415) 221-3777. It's close to Stanyan Street, which is the eastern border of Golden Gate Park. Prices: ten-speeds, $3 per hour, mountain bikes, $4 per hour. Or rent from Presidio Bicycle Shop, 5335 Geary Blvd., (415) 752-2453, which is near Park Presidio Boulevard. Prices: $7 per hour or $25 per day; helmet, $5 per day. Ride south in the boulevard's wooded margin and turn west inside Golden Gate Park.
Tips: Rent a mountain bike. With thick tires and upright handlebars, it's more stable and comfortable than a road racer. Wear a helmet. And take a jacket or sweater along; fog can roll through the city in the afternoon.
Where to ride: Buy a map for $3.50 called "San Francisco Biking-Walking Guide." One side has suggested bike routes through the city; the other is a grade map that shows by color intensity how steep each street is, so you can pick your own way around town. There's a map of Golden Gate Park in it, too.