One of America’s most beautiful and unusual swimming pools, built in 1923, is hidden behind pastel stucco walls and honored with a listing in the National Register of Historic Places. Two underground wells (meaning water’s definitely on the nippy side) feed the free-form lagoon, which is shaded by three-story Spanish porticos and has both fountains and waterfalls. During summer, the pool’s 820,000 gallons of water are drained and refilled nightly, thanks to an underground aquifer, ensuring a cool, clean swim. Visitors are free to swim and sunbathe here, just as Johnny Weissmuller and the late Esther Williams did decades ago. For a modest fee, your kids (or you) can learn to swim during special summer programs.