Walking: San Francisco rewards walking, and the areas that most visitors cover are easy (and safe) to reach on foot. However, many neighborhoods have steep—make that steep—hills. In some areas the sidewalk is carved into steps; a place that seems just a few blocks away might be a real hike, depending on the grade. When your calves ache, you're that much closer to being a local.
By Subway: BART is San Francisco's subway, limited to one straight line through the city. Within the city, it's a handy way to get to the Mission or perhaps Civic Center. BART is most useful for reaching the East Bay or SFO and Oakland's airport. There are no special visitor passes for BART; within town a ticket runs $1.85.
On Muni: Muni includes the city's extensive system of buses, electric streetcars, nostalgic F-line trolleys, and cable cars. The trolleys and cable cars are a pleasure for the ride alone, and they run in well-traveled areas like Market Street and, in the case of the cable cars, the hills from Union Square to Fisherman's Wharf. Basic fare for the bus, streetcars, and trolleys is $2.25; cable-car tickets cost $6 one-way. At $15, a one-day Muni Passport, which includes cable car rides, is a great deal.
By Car or Taxi: Considering its precipitous hills, one-way streets, and infuriating dearth of parking, San Francisco is not a good place to drive yourself. Taxis, however, can come in very handy. Call one or hail one on the street; they tend to cluster around downtown hotels. Ride companies like Lyft and Uber now do most of the taxi business in the city; hail one with their respective phone apps.