The secret's out -- I visited today and it was bustling with kids, dogs, and picnickers. Even with the crowd and some unsightly construction on the hillside, it's a lovely little nook.
Best Gurgling Spring San Francisco 2008 - El Polin
Considered a sacred site by the native Ohlone, who had inhabited a settlement near the spring for thousands of years until the Spanish founded the Presidio in 1776, El Polin is the epitome of tranquility these days. One reason: Few people bother to visit the out-of-the-way landmark, near a picnic area at the foot of Inspiration Point. Legend among early Spanish settlers was that any maiden who drank from its waters under a full moon would be blessed with twins; males likewise viewed it as a source of virility. Even the little spring's name, Polin, was a play on the brawny (some say phallic) rollers used to load cargo ships. We can't vouch for the Viagra factor, but El Polin's gentle gurgle on a sunny afternoon is tonic to the soul.