Wikipedia has this to say about the ruins:
"On March 14, 1896, the Sutro Baths were opened to the public as the world's largest indoor swimming pool establishment. The baths were built on the sleepy western side of San Francisco by wealthy entrepreneur and former mayor of San Francisco (1894–1896), Adolph Sutro. The vast glass, iron, wood, and reinforced concrete structure was mostly hidden, and filled a small beach inlet below the Cliff House, also owned by Adolph Sutro at the time. Both the Cliff House and the former baths site are now a part of the Golden Gate National Recreation Area and operated by the United States National Park Service."
Apparently, when it first opened there was a single large freshwater pool, 6 saltwater pool, slides, chutes, trapezes, diving platforms, over 500 dressing rooms and a museum filled with the fruits of Adolf Sutro's travels around the world. It was said that you could see just about anything when visiting the pools.
It was a short walk down the hill to the ruins and there you are allowed to wander freely, trying to imagine how a structure so huge and imposing could be boiled down to just a few concrete walls and a cave. We scrambled about on the rocky ledges and took a higher vantage point to overlook the Pacific. It was almost reminiscent of some of the overlooks I came across while in Cinque Terre.
Post-romp, we were a bit peckish and had lunch at the also famous Cliff House. The views were amazing, the chowder was delicious and chowdery, and most importantly we were able to wash our dirty hands and discuss the strange photo shoot we had seen earlier.