Although they may not be San Francisco's most practical means of transportation, cable cars are certainly the best loved and are a must-experience when visiting the city. Designated official historic landmarks by the National Park Service in 1964, they clank up and down the city's steep hills like mobile museum pieces, tirelessly hauling thousands of tourists each day to nowhere in particular.

London-born engineer Andrew Hallidie invented San Francisco's cable cars in 1869. He got the idea by serendipity. As the story goes, Hallidie was watching a team of overworked horses haul a heavily laden carriage up a steep San Francisco slope. As he watched, one horse slipped and the car rolled back, dragging the other tired beasts with it. At that moment, Hallidie resolved that he would invent a mechanical contraption to replace such horses, and just 4 years later, in 1873, the first cable car made its maiden run from the top of Clay Street. Promptly ridiculed as "Hallidie's Folly," the cars were slow to gain acceptance. One early onlooker voiced the general opinion by exclaiming, "I don't believe it -- the damned thing works!"

Even today, many visitors have difficulty believing that these vehicles, which have no engines, actually work. The cars, each weighing about 6 tons, run along a steel cable, enclosed under the street in a center rail. You can't see the cable unless you peer straight down into the crack, but you'll hear its characteristic clickity-clanking sound whenever you're nearby. The cars move when the gripper (not the driver) pulls back a lever that closes a pincerlike "grip" on the cable. The speed of the car, therefore, is determined by the speed of the cable, which is a constant 9 1/2 miles per hour -- never more, never less.

The two types of cable cars in use hold a maximum of 90 and 100 passengers, and the limits are rigidly enforced. The best views are from the outer running boards, where you have to hold on tightly when taking curves. Everyone, it seems, prefers to ride on the running boards.

Hallidie's cable cars have been imitated and used throughout the world, but all have been replaced by more efficient means of transportation. San Francisco planned to do so, too, but the proposal met with so much opposition that the cable cars' perpetuation was actually written into the city charter in 1955. The mandate cannot be revoked without the approval of a majority of the city's voters -- a distant and doubtful prospect.

San Francisco's three existing lines form the world's only surviving system of cable cars, which you can experience for yourself should you choose to wait in the endless boarding line (up to a 2-hr. wait in summer).