Sutro Baths

In 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, Adolph Sutro. The vast glass, iron, wood, and reinforced concrete structure was mostly hidden, and filled a small beach inlet below the Cliff House which was also owned by Adolph Sutro at the time.
A visitor to the Baths not only had a choice of 7 different swimming pools—one fresh water and six salt water baths ranging in temperatures—but could visit a museum displaying Sutro's large and varied personal collection of artifacts from his travels, a concert hall, seating for 8,000, and, at one time, an ice skating rink. During high tides, water would flow directly into the pools from the nearby ocean, recycling the 2 million US gallons (7,600 m³) of water in about an hour. During low tides, a powerful turbine water pump, built inside a cave at sea level, could be switched on from a control room and could fill the tanks at a rate of 6,000 US gallons a minute (380 L/s), recycling all the water in five hours.