You could probably find anything you'd ever want in an urban hike in San Francisco.
Want heart-pumping exercise? The city is hilly and, like Los Angeles, has lots of old city-owned staircase/sidewalks to take you up those steep slopes. Hike up the Filbert Steps of Telegraph Hill, or the famously twisty Lombard Street.
Want something a little less strenuous? There are beach trails (with fewer hills) along the San Francisco Bay. Want to experience nature? How do groves of redwoods and eucalyptus trees inside city parks sound, along with an abundance of public gardens?
As urban hiking has become more popular, the city of San Francisco has been working to restore and expand its approximately 30 miles (48.3 kilometers) of city trails. Popular hikes include short distances such as a leisurely stroll along Lobos Creek Trail in the Presidio park, or the mile and a half (2.4 kilometers) across (and then back, if you want) the Golden Gate Bridge, with great views of Alcatraz, the city skyline, Angel Island and the Pacific Ocean. If you want to take a longer, more strenuous excursion, then hike the entire 10-and-a-half miles (16.9 kilometers) of the California Coastal Trail.
The Golden Gate National Recreation Area includes trails in the Lands End area at the northwestern corner of the city with spectacular views of the water, shipwrecks and wildflower-covered hills. Hike through the Sutro Historic District with its gardens and see the ruins of the famous Sutro Baths, a 19th-century swimming pool complex. Your route might wind up at the historic Cliff House, a restaurant built in 1863, where it's often easy to watch seals on the rocks below.
The city and various organizations provide information about other hikes that will take you past such places as Chinatown, Fort Mason, outdoor murals and historical sites commemorating the 1906 earthquake. Just remember that when the fogs roll in, you won't see much, and that summer in San Francisco can be chilly.