It's Saturday afternoon and you're strolling through Golden Gate Park, near John F. Kennedy Drive and the Conservatory of Flowers, when you hear something unusual: the swooshing of jazz brushes on a snare drum. Seductive tenor sax drifts with the wind, and, wait, where the hell is that coming from? If you haven't experienced this, then you haven't spent enough time wandering along JFK Drive on weekend afternoons. A certain tunnel under the park thoroughfare near the Conservatory of Flowers is a favorite spot for Bay Area jazz musicians to gather for impromptu jams. The small concrete tube works as a kind of bandshell, sheltering the instruments' sounds from the breeze and even amplifying them slightly, just enough to be heard by pedestrians above. The jam makes a lovely surprise when wandering around the park, and even draws small audiences. But whether sticking around to watch or just floating in and out of the music, the jazz-tunnel jam is our favorite musical surprise in Golden Gate Park.