The Sutro Baths

"The Sutro Baths were a large, privately owned swimming pool complex in San Francisco, California, built in the late 19th century. The building housing the baths burned down in 1966 and was abandoned...
A visitor to the baths not only had a choice of seven different swimming pools—one fresh water and six salt water baths ranging in temperatures—but could also 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 two million US gallons 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, recycling all the water in five hours...
The baths struggled for years, mostly due to the very high operating and maintenance costs. Shortly after closing, a fire in 1966 destroyed the building while it was in the process of being demolished. All that remains of the site are concrete walls, blocked off stairs and passageways, and a tunnel with a deep crevice in the middle."