"Experience the National Parks bordering the Golden Gate. Join Ranger James Osborne for this fun and strenuous 12-mile loop bike ride that begins in the Presidio, spans the Golden Gate Bridge, then descends into the peaceful valley in the Marin Headlands. You will gain a unique perspective on the Bay Area Ridge Trail and the Golden Gate, and get a terrific workout! For experienced riders with hybrid bikes (10 miles is paved; 2 is dirt trail)."