Those taking a casual stroll along San Francisco’s marina could easily miss one of the city’s best kept secrets—especially if they fail to stop and listen.

The Wave Organ, an acoustic instrument built into a natural jetty, sits on the Bay near Crissy Field. Joggers, dog walkers and tourists frequent the small strip of land for its fantastic views of the city, Golden Gate Bridge and the Marin Headlands, but it’s the jetty’s intermittent haunting sounds that really make it worth a visit.

“This place isn’t about hearing, really. It’s about listening,” said Peter Richards, the Wave Organ’s designer and a senior artist-in-residence at the Exploratorium.

Built in 1986 using granite and marble from an old cemetery, the Wave Organ was designed to create music out of the natural environment. Twenty-five concrete pipes placed in the water capture the sounds of the ocean’s waves.

The result is an ethereal melody created by a phenomenon called “harmonic resonance.” As the waves push air in and out of the pipes, different sounds are generated depending on the volume of air in the pipes. The more air, the more guttural the sound. The less air, the higher the pitch. The Wave Organ can often sound like a long moan, burp or gurgle.

While the acoustics of the Wave Organ are its most notable attraction, Richards conceived of the sculpture as a way to get people to pay attention to their surroundings. If you listen closely, he said, the sounds of the wind, waves, foghorns, seagulls and city all meet to create a soundscape like no other. 

Richards also sees the Wave Organ as a place for reflection—and a good location to ponder San Francisco, a city that sits at the confluence of extreme adversity and prosperity. He hopes the instrument will help draw people a little closer together.

“One of my underlying aims was to get people to realize that we’re not singular, we’re all part of a big party,” he said.