The building at Washington and Mason Streets serves a dual purpose: museum and power station. The cable winding machinery occupies the ground floor, visible from galleries where visitors can watch the cables feed out through underground conduits to the streets. Three cable lines -- Powell-Mason, Powell-Hyde, and California Street -- all receive their motive power from this single facility. The sheaves are enormous, the cables thick as a person's wrist, and the sound is a continuous mechanical hum that visitors feel through the floor. The museum's exhibits provide context, but the machinery provides the spectacle.

The museum's collection includes historic cable cars dating to the system's 19th-century origins, antique grip mechanisms, photographs, and interpretive displays explaining how the cable car system works. Andrew Hallidie's original 1873 grip car, which made the first run down Clay Street hill, is preserved here. The exhibits trace the system's evolution from a practical solution to San Francisco's impossible gradients to its current status as a National Historic Landmark and the only remaining manually operated cable car system in the world. Vintage photographs show the extent of the original network, which once covered much of the city before the 1906 earthquake and the rise of motorized transit reduced it to its present three lines.

The Cable Car Museum charges no admission, a policy that makes it one of the best free attractions in San Francisco. Visitors can see, hear, and feel the machinery that makes the cable car system possible -- a rare opportunity to observe a 19th-century transportation technology still in daily operation. The museum gift shop sells cable car memorabilia, and a viewing gallery offers close-up views of the cable tension mechanisms. For anyone who has ridden a cable car and wondered what happens beneath the street, the museum answers every question with mechanical precision.