As one writer described it in a 2001 Sfgate article:
“Converted from military to recreational use in 1972, the headlands have become an outdoor haven for hikers, cyclists, equestrians, surfers, bird watchers and beach combers. For folks interested in military history, the old buildings at Forts Baker, Barry and Cronkhite, with their bunkers and batteries, are sources of abiding interest. For more than a century they served as a bastion against invasion of the Golden Gate, armed with everything from old muzzle-loading cannon and mortars to Cold War nuclear missiles. But most of the weapons, including the missiles, were never fired.”
Bay Area Hiker features some hikes in the area and Bay Nature highlighted the history and legacy of the Marin Headlands, luckily, “its protection is the result of happy accidents and the efforts of a few persistent people.” The Marin Headlands provide many vistas for pictures in addition to beautiful hiking areas.