Beneath your feet runs the operational heart of the only moving National Historic Landmark in the United States. The cable car system was invented by Andrew Hallidie in 1873, specifically to solve the problem of San Francisco's brutal hills. Before the cable cars, horses struggled and died trying to haul streetcars up grades that exceeded 20 percent.
Hallidie's genius was to run a continuously moving steel cable beneath a slot in the street and equip the cars with a grip that could clamp onto and release from the cable. The grip operator — called the gripman — controls the car's movement by working a large lever that engages the cable running at a constant nine and a half miles per hour beneath your feet. At its peak in the 1880s, San Francisco had eight cable car lines running 112 miles of track.
The automobile and electric streetcar reduced the system to three lines. When the city proposed eliminating the last lines in the early 1950s, a citizen named Friedel Klussmann organized a citywide campaign to save them, and San Franciscans voted overwhelmingly to keep the cars running. The cable car barn and museum here at Mason and Washington contains the actual machinery — the giant sheaves and engines that keep the cables moving under the entire city.