About an hour and a half north of San Francisco proper, Point Reyes is a popular day trip for great hiking and sea kayaking (there's also good camping here, though campsites can only be reached by foot so it's best to steer clear unless you have some backpacking experience). The park is famous for its historic lighthouse, which also happens to be an excellent place to whale watch and see elephant seals in the summer months. Point Reyes is home to some of the area's best hiking—we like to send first-timers to the Bear Valley Visitor Center, where you can find an education center and plenty of rangers to fill you in on interesting facts and help you get your bearings when it comes to the many hiking trails that leave from that point. History geeks might want to take a detour near the town of Inverness on the way up, where you can explore the beached remains of the SS Point Reyes, which shipwrecked in Tamale Bay more than 100 years ago. Remember to bring some cash to cover entrance fees.
Tennessee Valley Rd., Marin
The Tennessee Valley is in the same direction as Muir Beach (over the Golden Gate bridge and along Highway 101), and its' encyclopedic list of hiking trails is another excellent way to explore the Golden Gate Recreation area. Advanced hikers can explore the hills around the valley while beginners and families can take the almost two-mile trek to a little cove—locals know it's best to time a hike with the low tide when you can actually see the shipwrecked engine of the SS Tennessee, which sunk near the beach in 1853. In the spring, the valley is home to gorgeous wildflowers, including buttercups and poppies, and in the summer and through early fall you can find fruit on the blackberry bushes. Remember: No dogs allowed.
Highway 1, Marin
Just across Highway 101 and over the Golden Gate Bridge, Muir Beach is an easy (but still totally idyllic) day trip from the city. The beach itself is a classic Northern California cove, with tall rocks and green hills on either side and boulders jutting up from the shallows—the surrounding area is home to plenty of wildlife, too. In the colder months, take the long pedestrian trail from the parking lot to the coastal trail and hike along the cliffs, which offer gorgeous views of the beachfront; be sure to pack layers, as winds can get cold. In the warmer months, it's perfect for sunbathing, and there's even a clothing-optional sunbathing and skinny dipping area past the line of rocks on the northernmost end of the beach. Afterwards, grab lunch at the Pelican Inn, a traditional English-style pub in the tiny nearby town.