Fort Mason, Marina & Buchanan, 771-3738, www.fortmason.org
Lake Merced, Sunset & Lake Merced, www.lakemerced.org
Starting in late summer, the city is liberally dotted with blackberry bushes loaded with tempting, juicy fruit. But since many of these bushes grow in areas where they're constantly dirtied by car exhaust, their fruit is often unfit for eating (it seems obvious to recommend that you avoid the bushes growing along the Great Highway, for instance). Intrepid city trekkers, however, know that there are numerous natural spots where you can pick as much as you please without fear of contamination. In fact, practically any verdant locale within sight of a body of water hosts at least a few blackberry vines. Our favorite spots are the hills above Fort Mason (mount the steps stretching up from the bay and you'll find the pathways festooned with fruit) and the shores of Lake Merced. Bring a pair of stout gloves and a bucket or two and pick away; you'll find yourself mostly alone as you harvest. A good wash is all the berries need to be edible. Fledgling Martha Stewarts may also want to consider turning the bounty into gleaming jars of jam, which make one hell of a hostess gift year-round.