The Powell-Mason line (shown as line PM on the Muni map) is the oldest of San Francisco's three surviving cable car routes, running essentially unchanged since it opened in early March 1888 under the Ferries and Cliff House Railway Company. It was the city's first north–south line to link Downtown directly to North Beach over Nob Hill, and the San Francisco Municipal Transportation Agency (SFMTA / Muni) describes it as the city's only transit line to operate virtually unchanged since opening day — likely the world's oldest continuously operated cable car line.

The 1.6-mile (2.6 km) route climbs from the Powell & Market turntable up Powell Street, over Nob Hill past the Mason Street car barn, and down Mason and Taylor streets to a turntable at Bay & Taylor, a few blocks from Pier 45 and Fisherman's Wharf. Unlike many lines that were converted to streetcars after the 1906 earthquake and fire, the Powell-Mason line was kept because no other vehicle of the era could manage its steep grades; an attempt by the mayor to replace the cars with buses in 1947 was beaten back in a famous "cable car war."

San Francisco's cable cars are the world's last manually operated cable car system and were designated a National Historic Landmark on January 29, 1964 (added to the National Register of Historic Places on October 15, 1966). The grip and conductor still work each car by hand, and at each end the single-ended cars are turned on manually powered turntables.

The best on-board views come on the North Beach side of Nob Hill: as the car heads north past Vallejo Street and descends toward Mason & Greenwich, the bay, Alcatraz Island and Angel Island open up ahead. Look east near Mason & Columbus for Coit Tower on Telegraph Hill. The manually operated turntables at the Powell & Market and Bay & Taylor terminals are the best places to photograph crews spinning the cars by hand. Riding on the outer running boards gives unobstructed shots, but mind your camera and your grip on the steep descents.

For railfans, the Powell-Mason line is living 19th-century technology still in daily service. Cars are gripped to a continuously moving steel cable running in a slot beneath the street; the gripman clamps and releases the cable to move and stop, while a separate conductor works the brakes and bells. The cable runs at a constant 9.5 mph (15.3 km/h), so that is the line's top speed. Track gauge is the system-wide 3 ft 6 in (1,067 mm).

The Powell lines use single-ended cars — they have a grip and controls at one end only — which is why each terminal has a turntable where the crew physically push the car around to face the other direction. The Powell-Mason and Powell-Hyde lines share a roster of 28 single-ended cars; some wear historic liveries such as Car 25's United Railroads paint scheme. The whole system is wound from the powerhouse at 1201 Mason Street, where the Cable Car Museum lets you watch the giant sheaves reeling the cables in and out directly above the route.

The line is also a direct link to the invention of the cable car: Andrew Smith Hallidie launched the first successful cable street railway, the Clay Street Hill Railroad, in San Francisco in 1873, and the Powell-Mason line opened just 15 years later on the same principle.

Expect a short, steep, noisy and thoroughly mechanical ride rather than a smooth tram trip — the hum of the cable underfoot, the clang of the bell, and the smell of the pinewood brake pads are part of the experience. The one-way trip takes roughly 16–17 minutes end to end, climbing Nob Hill before dropping toward the bay.

Cable cars are among San Francisco's most popular attractions, so be prepared for queues, especially at the Powell & Market turnaround and at Bay & Taylor on weekends and through the summer. Waits at the terminals can run long; many regular riders skip the queue by walking a block or two up the line and boarding at an intermediate stop, though there is no guarantee of a free spot. You can ride seated inside, stand in the open-sided center section, or — for the classic thrill — hold the poles on the outer running boards as the car crests the hills.