Munching on a plump, juicy hot dog fresh from the steamer is one of the undying pleasures of urban living. From the Mission to the ballpark to Union Square, the fragrance of frankfurters, mustard, and sauerkraut is an irresistible contrapunto to the asphalt jungle's exhaust fumes and cheap cologne. So it's a bit surprising to find some of the town's finest hot dogs in the sylvan setting of Golden Gate Park. The Happy Belly cart, located near the entranceway to the Music Concourse, serves up an all-beef frank that's smoky and robust alongside a luscious chicken-apple dog bursting with sweet 'n' salty flavor. The crowning touch, though, is the stuff that tops off the dogs: light-textured Kewpie Japanese mayo and a peppery, eye-opening kimchi. The kimchi (prepared at Namu restaurant a few blocks away at Sixth Ave. and Balboa) has the tart, bracing edge of a really good sauerkraut; in concert with the dog and the Kewpie, it's sweet, spicy, sharp, and creamy all at once. Enjoying a Happy Belly on a Sunday afternoon while the Lindy in the Park dancers practice just up JFK Drive makes for a great country outing.