San Francisco cable cars have an unusual drive mechanism to go up and down the steep hills. A cable runs under the street, down the steep hill to the bottom, around a pulley, and back up to the powerhouse at the top. When the cable car wants to ascend, it clamps onto the cable and the engine at the top of the hill pulls it up.

You can see the powerhouse with its engines and giant wheels what have pulled cable cars up and down the hills for 150 years.