Philadelphia is full of carefully hidden secrets, one of which is a set of abandoned swimming pools underneath the Fairmont Water Works.
Originally built in 1793, the Fairmont Water Works has almost a century and a half of history before the swimming pools were constructed. The Water Works made Philadelphia the first city in the U.S. to bring fresh water to its citizens, and quickly became one of the most popular tourist attractions of the mid-19th century. However, pollution of the Schuylkill River forced the Water Works to close in 1909, which is when the buildings were converted into an aquarium.
The swimming pools were built in 1961, but only lasted 10 years, as flooding from Hurricane Agnes in 1972 forced the pools to close.
The pools were inoperable and hidden from the public for 20 years before they were uncovered during a restoration project in the 1990s. These pools may have been abandoned, but they're certainly not forgotten: Online media outlets like Thrillist have helped bring them back into the public eye, and the 2013 Philadelphia Hidden City Festival opened the pools to the public for a brief period.