Sutro Bath, opened in 1896, was the largest indoor swimming pool complex in the world. The complex utilized Pacific Ocean water to fill its pools. It burnt down in 1966 and was closed ever since. Its ruin is still around and becomes part of Golden Gate National Recreation Area.
Sutro Bath in its heydays.
Another view of the Sutro Bath ruin. The hump of rock at the back is the seal rock where the sea lions at Pier 39 used to hang out before the 1989 earthquake.
There is a tunnel at one side of the bath. It was used to pump seawater into the pools during low tide.
The end of the tunnel runs directly into the ocean.