BERKELEY If you are looking for a low-key day trip to the Bay Area, one that boasts a buffet of low- and no-cost activities for adults and children alike, consider following the locals' lead and going to Tilden Park. Spread over 2,077 acres of hills adjoining Berkeley's northeastern edge, Tilden is a dream come true for parents who have young children and also holds great promise for picnickers, plant lovers, hikers and swimmers. Oakland resident Sylvia Colt, who has a 7-month-old son, takes full advantage of the park's proximity and attractions. "I jump into my car and within five minutes I am at the park, which is full of trails for any type of hike you want," says Colt, who teaches math at Bancroft Middle School in San Leandro.