San Francisco

Bikes can be rented from around the northern waterfront Pier 41/Fisherman's Wharf/Aquatic Park area or near Golden Gate Park for trips to Marin County via the Golden Gate Bridge. Stanyan near Haight at the end of the park has several good shops.Golden Gate Transit also sporadically serves the North Bay from San Francisco, and has bike racks on most buses.

Nearby destinations suitable for day trips include:

Oakland
— A diverse and vibrant city, Oakland was once considered San Francisco's "sister city," and has been regaining that title in recent years due to a general renaissance of the city. Although not a major tourist destination, it's worth a visit for its many distinct and charming neighborhoods.
Berkeley
— Home to the University of California, Berkeley and one of the nation's most progressive communities. Also a hub of liberal political activism for the past several decades. It is also home to quite a few superb restaurants.
Sausalito
— Enjoy a ferry ride across the bay to beautiful Sausalito where you can walk along the water and admire the San Francisco skyline. Stroll to the waterfront restaurants, shops, and galleries.
Healdsburg
— A charming Wine Country town located among some of California's greatest wine appellations: Alexander Valley, Dry Creek Valley, Russian River Valley and Chalk Hill. Relaxed yet sophisticated atmosphere, with excellent restaurants, shopping and wine tasting. About 70 miles north of the Golden Gate Bridge.
Napa Valley
— The main wine growing region in the United States, a trip to the many wineries makes for a fun day, while those wanting a longer adventure can relax in any one of the many spas, bed and breakfasts, or other lodging options.
Muir Woods
— A 560 acre forest of old-growth redwood trees located in Mill Valley just north of the Golden Gate Bridge, Muir Woods is a pleasant respite from the city, and accessible by Golden Gate Transit on summer weekends.
Point Reyes National Seashore
— Located just north of San Francisco along the Pacific Coast Highway State Highway 1, Point Reyes is a beautiful seashore that is particularly nice to visit when gray whales are migrating along the coast, usually best in mid-January and then from March through May.
Peninsula
Just south of San Francisco, the peninsula has excellent nature preserves. Palo Alto — On the Peninsula south of the city, Palo Alto has some of the richest neighborhoods in all of California and makes for a beautiful drive with views of the coastline and magnificent mansions. Burlingame — Another well off neighborhood on the Peninsula, Burlingame has a lovely downtown area with plenty of shops, dining and streets lined with cypress trees.
Monterey
— An otherwise quiet beach town home to one of the country's best aquariums.
Santa Cruz
— Located on the coast north of Monterey Bay, this funky town is home to surfers, the beautiful and tech-savvy University of California, Santa Cruz, and a popular boardwalk. The Santa Cruz Mountains north of town are a great place for outdoor recreation such as hiking, and home to misty forests of famous, enormous redwood trees.
Vallejo
— Home to a wildlife theme park, Six Flags Discovery Kingdom.
Yosemite National Park
— Tours from San Francisco make for a wonderful day trip, although you will spend around 10 hours travelling for less than 4 in the park. Make sure to visit the amazing Giant Sequoias.
Lake Tahoe
— Buses and one Amtrak train per day link the Bay Area to nearby Truckee, and as with Yosemite, travel even by car to and from would consume much of the day. However, the spectacular alpine setting and winter ski and snowboard options surrounding the Lake make Tahoe an unforgettable destination.
Livermore
— A suburban city in the East Bay region of the San Francisco Bay Area. The Livermore Valley is "wine country", and produces some of California's best wines.