The Sutro Baths in San Francisco were opened in 1896, and for decades comprised the world’s largest indoor swimming pool. Built by wealthy entrepreneur Adolph Sutro, the baths were incredibly popular but struggled due to the massive costs associated with maintenance and operations.
The baths contained saltwater pools which drew water from the nearby ocean. There was also one freshwater pool. The structure burned down in 1966, though ruins from the building remain as a reminder of the past.