The Twin Peaks Tunnel is a 2.27-mile (3.65 km) long light rail/streetcar tunnel in San Francisco, California. The tunnel runs under Twin Peaks and is used by the K Ingleside/T Third Street, M Oceanview and S Shuttle lines of the Muni Metro system.

The eastern entrance to the tunnel is located near the intersection of Market and Castro streets in the Castro neighborhood, and the western entrance is located at West Portal Avenue and Ulloa Street in the West Portal neighborhood. There are two stations along the tunnel, Forest Hill near the western end, and the now disused Eureka Valley near the eastern end.